Pro-Russian insurgents have captured three government bases in eastern Ukraine, as the president-elect promised new initiatives to help end the mutiny in the country's industrial heartland.
Petro Poroshenko, speaking in Warsaw after meeting with President Barack Obama and other Western leaders, rejected a call from Ukraine's interim authorities to introduce martial law in the restive east, saying he would seek to pacify the region with an offer of amnesty and a promise of early regional elections.
Poroshenko's overture, expected to be detailed in his inaugural address on Saturday, came as the Ukrainian troops suffered a series of embarrassing setbacks on Wednesday.
National Guard forces ran out of ammunition and had to flee their base near the eastern city of Luhansk after hours of battle in which six militants were killed and three Ukrainian servicemen were injured.
The defeat came as rebel forces seized a border guard headquarters on the city's outskirts after besieging it for two days, then forced guards out of another base in the nearby town of Sverdlovsk on the Russian border. The guards there were granted safe passage and left with their weapons.
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The setbacks highlighted the ineffectiveness of Ukraine's badly trained and cash-starved armed forces, which also have been plagued by bad communication and poor supply lines.
Ukraine's provisional authorities have blamed the recent military failures on pro-Russia former President Viktor Yanukovych, claiming that his corrupt government starved soldiers of resources and training.
The fund shortage is so desperate that the Defence Ministry had to set up a charity account to support the armed forces while volunteers across the country have been buying provisions for the soldiers.
Obama, in Warsaw for a celebration on the 25th anniversary of Poland's first partially free election, praised Poroshenko for reaching out to the east, while offering $US5 million ($A5.41 million) in new aid for Ukraine's military - for equipment that could help in the fight against the insurgents.
The White House said the aid would include, for the first time, body armour and night-vision goggles for the use of troops. The US already has provided ready-to-eat meals and money for medical supplies and other non-lethal assistance, including clothing, sleeping bags and generators.
Many Ukrainian units in the east are manned by poorly-trained conscripts, who come from the region and appear reluctant to engage the rebels.
In the skirmishes overnight into Wednesday, Alexei Toporov, a spokesman for the insurgents in Luhansk, said the guards were fleeing, and the insurgents did not try to detain them.
"We released them and let them go home, we impeded nobody," he said. "They left their weapons, and this base is now coming under the control of the Luhansk People's Republic."
A rebel fighter who gave only his first name, Andrei, said the insurgents wanted to create a "humanitarian corridor" that would allow civilians to flee to Russia to escape the fighting.
An Associated Press reporter saw pro-Russian militia carrying crates of ammunition and explosives out of the base on Wednesday and driving away in border guards' cars. Ukraine's Border Guard Service said that the troops from that outpost had been evacuated to unspecified "safe locations".
