London ( CNN ) -- UK police arrested four people Tuesday on suspicion of traveling to Syria or supporting the fighting there . Two men , ages 29 and 18 , and a 21-year-old woman were arrested in Manchester , northwest England , on suspicion of being involved in the commission , preparation or instigation of acts of terrorism , Greater Manchester Police said . A fourth person , a 29-year-old man , was arrested in Oxford on the same charge , a police statement said . All four are now being questioned by counterterror officers in Manchester . Detective Chief Superintendent Tony Mole , head of the counterterror unit , said there was no imminent threat to anyone in Manchester or Britain . `` The operation has been running since autumn 2013 , since we first became aware of a number of individuals traveling from the northwest to the battlefields of Syria , '' he said . Mole said even those who travel to the region with the intention of providing humanitarian aid are putting themselves in danger . `` We know that some have already lost their lives or been detained by the regime and badly treated , '' he said . `` There are serious concerns that anyone traveling to Syria , whether for humanitarian reasons or because of a desire to support the Syrian opposition , may be targeted by extremist groups who want to recruit them . This could have serious repercussions for the safety of the individual concerned . '' Syria 's civil war will this month have dragged on for three painful years . More than 100,000 people have died and more than 680,000 others have been wounded , the United Nations has said . At least 6.5 million have been internally displaced and nearly 2.5 million people have fled to other countries . CNN 's Carol Jordan contributed to this report .
Four people are arrested by UK police on suspicion of Syria-related terror offenses . The three men and a woman are being questioned by counterterror officers in Manchester . - A man is shot dead at the entrance to an Ariana Grande concert in Manchester, England.