Media playback is unsupported on your device Media caption On Sunday, Turkish troops fired tear gas at the Syrian border, as Mark Lowen reports 
 
 Turkey has begun to close some of its border crossings with Syria after about 130,000 Kurdish refugees entered the country over the weekend. 
 
 On Sunday Turkish security forces clashed with Kurds protesting in solidarity with the refugees. Some protesters were reportedly trying to go to Syria to fight Islamic State (IS). 
 
 Most refugees are from Kobane, a town threatened by the advancing militants. 
 
 IS has taken over large swathes of Iraq and Syria in recent months. 
 
 Before the latest influx, there were already more than one million Syrian refugees in Turkey. They have fled since the start of the uprising against Syrian President Bashar al-Assad three years ago. 
 
 Some of the new arrivals are being sheltered in overcrowded schools, as Turkey struggles to cope with the influx. 
 
 'Huge numbers' 
 
 On Friday Turkey opened a 30km (19-mile) section of the border to Syrians fleeing the town of Kobane, also known as Ayn al-Arab. 
 
 But on Monday only two out of nine border posts in the area remained open, the UN refugee agency UNHCR said. 
 
 Mark Lowen, BBC News, southern Turkey 
 
 Turkey was already struggling to cope with over a million Syrian refugees - that was before 130,000 more fled across the border at the weekend. The sheer numbers would overwhelm any country. 
 
 Added to that, they are Kurds from Syria, many of them deeply hostile to Turkey. For 30 years, Turkish forces fought Kurdish rebels in a civil war that killed 40,000 people. 
 
 The fact that Turkey is accepting tens of thousands of Kurds is a sign of how allegiances are being forced to change with the onslaught of Islamic State. But deep-seated tension between Kurds and Turks have again come to the surface, leading to Sunday's border clashes. 
 
 Turkey fears that Kurds will cross into Syria to join the Kurdish militia. The worry is that, renewed by fresh recruits, it could ally with the outlawed PKK and launch attacks on Turkish soil. All the regional complexities, added to the refugee influx, make for a precarious situation here. 
 
 Clashes broke out on Sunday after a demonstration by Kurds on the Turkish side of the border. 
 
 Some protesters threw stones at security forces, who responded with tear gas and water cannon. There were no reports of serious injuries. 
 
 Turkish security forces were trying to stop Kurdish fighters from entering Syria to take part in the defence of Kobane, says the BBC's Mark Lowen at the scene. 
 
 The Kurdistan Workers' Party (PKK), a banned militant group that fought a civil war for autonomy within Turkey for decades, has called on Kurds to join the fight against IS. 
 
 Our correspondent says the Syrian conflict has reawakened old hostilities and shaken a fragile peace between Kurds and Turkish authorities. 
 
 PKK-affiliated forces have been battling IS in northern Iraq for months. 
 
 Image copyright Reuters Image caption Most of the border crossings from Syria to Turkey are now closed 
 
 Image copyright AP Image caption Turkish security forces clashed with demonstrators at one crossing on Sunday 
 
 Carol Batchelor, a spokeswoman for the UN refugee agency in Turkey, told the BBC that the country needed urgent aid to cope with the influx - including food, blankets and winter clothing, "particularly for children". 
 
 In other developments: 
 
 A Syrian government air strike killed at least 42 civilians in rebel-held territory in the north-western province of Idlib on Sunday, activists said 
 
 IS issued a statement urging its supporters to kill "disbelievers" from the countries that have joined a international coalition against the group 
 
 US Secretary of State John Kerry and Iranian counterpart Mohammad Javad Zarif discussed the threat posed by IS during a meeting in New York on Sunday, a US official said 
 
 IS is closing in on the predominantly Kurdish town of Kobane, having seized dozens of villages in the area in recent days. 
 
 It began the assault on Tuesday, and by Sunday militants were about 10km (six miles) away, said the Syrian Observatory for Human Rights. 
 
 Reports suggest that IS has used heavy weaponry, including tanks, in the attack. 
 
 The US has said it will attack the group in Syria as part of a strategy to destroy it, though so far it has carried out air strikes against IS only in Iraq. 
 
 Media playback is unsupported on your device Media caption Tony Blair: " Isis... kill without mercy and they're prepared to die without regret" 
 
 Attacking IS in Syria is considered more complicated, partly because of the strength of the country's air defence system and because foreign strikes do not have the approval of President Assad. 
 
 Former UK Prime Minister Tony Blair told the BBC on Sunday that air strikes alone might not be enough to contain the group. 
 
 "If necessary, we shouldn't rule out the use of, particularly, special force capabilities," he said. 
 
 President Obama has previously ruled out the involvement of US ground troops, and has instead promised to provide arms and training to local forces fighting against IS. 
 
 Who are Islamic State (IS)? ||||| BEIRUT Syrian Kurdish fighters have halted an advance by Islamic State fighters to the east of a predominantly Kurdish town near the border with Turkey, a spokesman for the main armed Kurdish group said. 
 
 "Fierce clashes are still under way but the ISIS (Islamic State) advance to the east of Kobani has been halted since last night," Redur Xelil, spokesman for the main Kurdish armed group, the YPG, said via Skype. 
 
 He said the eastern front was the scene of the fiercest fighting in the offensive launched by Islamic State last Tuesday on Kobani, also known in Arabic as Ayn al-Arab. More than 100,000 Syrian Kurds, driven by fear of Islamic State, have fled its advance, many crossing the border into Turkey. 
 
 The Syrian Observatory for Human Rights, which tracks violence in the Syrian war, said Islamic State fighters had made no significant advance in the last 24 hours. 
 
 The offensive is Islamic State's second attempt to take Kobani since June, when it staged a lightning advance across northern Iraq, seizing the city of Mosul and with it Iraqi weaponry including American-made hardware that the Syrian Kurds say is now being used against them. 
 
 The previous attack on Kobani, in July, was fought off with the help of Kurds who crossed the border from Turkey. Xelil said hundreds had crossed from Turkey again to help repel the current offensive. 
 
 "There have been no reinforcements apart from some Kurdish youths from Turkey," he said. 
 
 The United States has launched air strikes against Islamic State in Iraq and has said it will not hesitate to strike the group in Syria, but wants allies to join its campaign. 
 
 The United Nations said on Sunday the number of Syrian Kurds who had fled into neighboring Turkey alone might have topped 100,000 and was likely to go much higher. 
 
 "There are still clashes to the west and south of Kobani but not at the same intensity as the eastern front," Xelil said. 
 
 Rami Abdulrahman, who runs the Observatory, said Islamic State had made "no progress worth mentioning" in the past 24 hours, but that clashes were "at their most intense". 
 
 There were conflicting accounts of how far Islamic State fighters were from Kobani. Xelil said they were 20-30 km (12-19 miles) away, while Abdulrahman said they were around half that distance from the town. 
 
 (Reporting by Tom Perry; Editing by Kevin Liffey)
– Up until the middle of last week, Turkey put the number of Syrian refugees within its borders at more than a million. That number has swelled by 130,000 in the last four days, according to Turkey's deputy PM. It's not just the sheer number of refugees that's noteworthy: They're mainly Kurds, and as the BBC reports, many are "deeply hostile" to Turkey. And since Thursday, they've been pouring into the country in an attempt to flee ISIS militants who have, as the AP puts it, "pushed the conflict nearly within eyeshot of the Turkish border." The current conflict centers around the town of Kobani, which ISIS attempted to take in July, reports Reuters. That attempt was quelled with the help of Kurds who entered Syria from Turkey, and there were skirmishes on the Turkish side of the border yesterday as the country tried to prevent Kurds from flowing into Syria once again. As BBC correspondent Mark Lowen explains, there's a fear that the Kurdistan Workers' Party, which for decades battled for autonomy for Kurds inside Turkey, could team up with a beefed-up Syrian Kurdish militia and once again take up arms within Turkey. For now, the Syrian Kurdish fighters are said to have halted an ISIS advance on Kobani from the east, according to a rep for the Kurdish group, who says that's the front where the most intense fighting is taking place.