positions in Sloviansk, which were under heavy siege by government forces. The insurgents later offered to exchange hostages, including the local police chief, for weapons. Second government counter-offensive Government forces focused primarily on Sloviansk for the next few days. However, on 25 April, a military helicopter at the Kramatorsk airfield exploded after its fuel tank was shot while it was taking off. Insurgents claimed responsibility for the shooting, and said that they had hit the helicopter with a rocket propelled grenade in an interview with Russian media. Dmitry Tymchuk, a defence expert and director of the Centre of Military and Political Research in Kyiv, told reporters that the Mi-8 helicopter pilot had managed to escape with minor injuries. A transport aeroplane was also reportedly destroyed. After having recaptured many formerly occupied buildings in Sloviansk during a renewed offensive there, Ukrainian forces successfully captured a television transmission tower in Kramatorsk on 2 May. Further clashes between the Ukrainian army and insurgent fighters overnight on 2–3 May led to the death of ten pro-Russian activists, and left thirty injured, according to a local pro-Russian self-defence leader. During the fighting, the Ukrainian army was able to remove the insurgents from the Security Service of Ukraine (SBU) building that they had been occupying. Street battles broke out, and Russian media reported that the city was mostly under the control of Ukrainian forces, with only the city square remaining under pro-Russian control. However, it was reported the next day that the building had been abandoned by government forces, rather than fortified, and that the flag of the Donetsk People's Republic still flew from it even after the insurgents had been evicted. This eviction did not last long, as the Ukrainian army abruptly withdrew back to their positions at the military airfield on 4 May. Insurgents then reclaimed the SBU building and police station that had been abandoned by Ukrainian forces. During the day, clashes erupted between insurgents and an army column on a road near Kramatorsk, which left one civilian dead. A Ukrainian army unit was ambushed near Kramatorsk by about thirty DPR soldiers on 13 May. The ambush was initiated when DPR forces fired a rocket-propelled grenade at an armoured personnel carrier that had been carrying paratroopers, causing the vehicle to explode. Many soldiers were injured in the ensuing skirmish, and seven soldiers were killed, along with one separatist. A government mortar carrier was