Pro-Russian separatists in eastern Ukraine have shot down a military helicopter in Slovyansk, killing 14 people including an army general, as rebels and government forces fought fierce battles.
In the capital Kiev, Ukraine's acting president said rebels used surface-to-air missiles to take down the helicopter, which had been ferrying servicemen including General Serhiy Kulchytskiy, who was among the dead.
"I just received information that near Slovyansk, the terrorists - using a Russian man-portable air defence system - shot down our helicopter," Oleksandr Turchynov told parliament.
Slovyansk is in the Donetsk region, one of the two provinces in eastern Ukraine that have declared independence from the government in Kiev.
A separatist spokesman had earlier on Thursday told Russian news agencies that the fighters had downed a Ukrainian army helicopter in a fierce battle that was still raging on the southern outskirts of the rebel-controlled city.
The unnamed spokesman said that "as a result of active military activities, several houses belonging to civilians caught fire".
Elsewhere in eastern Ukraine, a convoy of pro-Russian separatists headed towards the Donetsk airport which government forces recently recaptured.
The airport was the scene of heavy fighting that killed dozens of pro-Russia fighters earlier in the week. The government claims it has taken control of the site, but the separatists have taken the road leading to it.
"Clearly that convoy was heavily loaded with weapons and ammunition," Al Jazeera's David Chater, reporting from Donetsk, said. "They are ready for a fight here."
As separatists began holding funerals for dozens of fighters killed in the battle for the airport, the self-proclaimed prime minister of the Donetsk People's Republic, Aleksander Boroday, told families of the dead that he and his supporters were "prepared for more fighting".
Speaking in front of relatives gathered at the Kalininsky Hospital morgue, he said he hoped he would not have to request "more assistance" from Russia, Al Jazeera's John Wendle in Donetsk reported.
Kiev says Russia is sending troops to fight separatists. Moscow denies the accusations, saying it has no influence over rebels.
Meanwhile, a rebel leader in Slovyansk said his fighters were holding four observers from the Organisation for Security and Cooperation in Europe (OSCE) and promised that they would be released imminently.
Vyacheslav Ponomarev, the self-proclaimed "people's mayor'' of Slovyansk, said the monitors who are from Turkey, Switzerland, Estonia and Denmark were safe.
The OSCE said it had lost contact with one of its four-man monitoring teams in Donetsk on Monday evening.
Rebels in Donetsk and Luhansk regions have pleaded to join Russia, but President Vladimir Putin has ignored their appeal in an apparent bid to de-escalate tensions with the West and avoid a new round of Western sanctions.