Armored personal carriers driven into the eastern Ukrainian city of Slaviansk had been under the control of Ukrainian armed forces earlier on Wednesday, pictures taken by Reuters photographers showed.
A soldier guarding one of six troop carriers now under the control of pro-Russian separatists told Reuters he was a member of Ukraine's 25th paratrooper division from Dnipropetrovsk.
"All the soldiers and the officers are here. We are all boys who won't shoot our own people," said the soldier, whose uniform did not have any identifying markings on it.
Armored personnel carriers marked with the numbers 815, 842 and 847 were among six under Ukrainian control in the center of Kramatorsk early on Wednesday. They were seen under the control of pro-Russian separatists in the center of Slaviansk later.
A civilian in Kramatorsk who identified himself as Felix told Reuters he had seen Ukrainian forces give up their vehicles to armed pro-Russian separatists.
A spokesman for the pro-Russian separatists in Slaviansk said the Ukrainians had given up after talks. It was not clear whether there was any threat of force.
Ukraine's defense minister, Myhailo Koval, was travelling to the Donetsk region to establish what is happening, deputy prime minister Vitaly Yarema told journalists in Kiev.
Meanwhile, dozens of masked pro-Russian separatists armed with Kalashnikov assault rifles have seized control of the city hall in the eastern Ukraine city of Donetsk demanding a referendum, a local government spokesman said.
The three dozen men in mismatched camouflage gear and carrying assault and hunting rifles, pistols and knives took over the building at 0700 GMT, Donetsk city spokesman Maxim Rovinsky said.
The men have started assembling barricades, but are allowing people to enter and leave the building and have agreed not to interfere with the work of the regional parliament, he added.
There were no obvious signs of barricades around the building, according to a Reuters witness.
Donetsk is the capital of a region that has become the focal point of Ukraine's standoff with separatist pro-Russians in its industrial east and southeast.
Earlier, Ukraine's Prime Minister accused Russia of "exporting terrorism" to Ukraine by using covert forces to organize armed separatists who he said had attacked Ukrainian forces and occupied state buildings.
"The Russian government must immediately call off its intelligence-diversionary groups, condemn the terrorists and demand that they free the buildings," Arseny Yatseniuk told a government meeting.
NATO
Military alliance NATO said on Wednesday it had decided on a series of immediate steps to reinforce its forces in Eastern Europe because of the Ukraine crisis.
"You will see deployments at sea, in the air, on land to take place immediately; that means within days," NATO Secretary-General Anders Fogh Rasmussen told a news conference after the decisions were taken by NATO ambassadors.
NATO fighter aircraft will fly more sorties over the Baltic region, allied ships will deploy to the Baltic Sea, the eastern Mediterranean and elsewhere, and allied military staff will be sent out to improve NATO's preparedness, training and exercises, Rasmussen said.
UN
It is not the right moment for any United Nations peacekeeping troops to be sent to Ukraine, U.N. Secretary General Ban Ki-moon was quoted as saying on Tuesday.
"At this moment, it doesn't seem very practical to send troops," Ban told Mexican newspaper Reforma, according to the Spanish text of an interview.
Ban, who was in Mexico City to attend a conference on international development, was speaking as Ukrainian forces launched a "special operation" against separatist militia in the Russian-speaking east of the country.
Tensions have flared between Moscow and the West in Ukraine since Russia's annexation of the Crimean region last month after the overthrow of Ukraine's Moscow-backed president, Viktor Yanukovich.
Ban told the newspaper that any decision to send troops to Ukraine would need to be agreed by the U.N. Security Council, of which Russia is a permanent member.
"Unless we have a clear mandate and authorization from the Security Council, I can't take any action," Ban said.
REUTERS