At the end of day-long talks in Geneva all parties seemed to step back from the precipice, following fast moving events in Eastern Ukraine is our International Editor Lindsey Hilsum in Donetsk.
The west said Russia is aiding the pro-Russian activists occupying buildings.
A crowd of around 300 men armed with stun grenades and Molotov cocktails attacked the base, in the south-east part of the country late on Wednesday, the interior ministry said in a statement.
Servicemen inside fired warning shots but the assault continued and the army had to respond, it said. There were no casualties among the Ukrainian servicemen, the ministry said, and 63 attackers were detained.
A single grey police jeep was inside the compound on Thursday morning with broken windows, flat tyres and bent doors. The gates of the compound had been flattened. There were shell casings outside the gates and several unused petrol bombs.
Police major Oleksandr Kolesnichenko, deputy commander of the base, said: “They came here around 8.15pm, demanding that we surrender our weapons and join the people. There were some women with them, but then they left.
“Then they used a truck to break through the gate. There was some incoming fire, I could not see who was shooting it was dark,” he said. “We fired first in the air. We fired warning shots after they entered the compound. We had no casualties. We are safe.”
With tens of thousands of Russian troops deployed along the border with Ukraine, there are fears the Kremlin might use the instability in the predominantly Russian-speaking region as a pretext for seizing more territory beyond its annexation of Crimea last month.
Ukraine’s military operation against separatists has hit obstacles. Called an “anti-terrorist” operation by the Kiev government, it started on Tuesday and is designed to dislodge pro-Russia gunmen from local authority buildings in a swathe of cities and towns in eastern Ukraine.
Pro-Russian activists want referendums on greater autonomy for the south-east or the right to join the Russian Federation.
But in several locations, Ukrainian troops met vehement opposition on Wednesday from pro-Russia supporters, who object to the new government in Kiev.
Foreign ministers from east and west were trying to defuse the Ukraine crisis on Thursday in Geneva, but risk being upstaged by Russian President Vladimir Putin.
With Russian troops massed on the border with Ukraine, prospects of significant progress at the four-way talks appear slim. By contrast, what Mr Putin said during his annual “hotline” session with the Russian people may have far greater influence on events in Ukraine’s rebellious east.
During the televised Q&A, Mr Putin said Ukraine’s decision to send armed forces into eastern Ukraine instead of trying to establish a dialogue with the Russian-speaking population there was a “grave crime.”
Mr Putin said crisis talks being held in Geneva were “very important” and urged the government in Kiev to sit down to talks with Russian-speaking communities in the east of the country.
It’s all nonsense. There are no kinds of Russian units in eastern Ukraine – Vladimir Putin
He said claims that Russian forces were present in east Ukraine were “rubbish”.
“It’s all nonsense. There are no kinds of Russian units in eastern Ukraine. No special forces, no instructors. They are all local citizens,” he said.
Mr Putin accused the Ukrainian leadership of talking only to its own appointees in the troubled eastern regions instead of opening what he called a genuine dialogue with the people.
Extending the crisis?
During a televised session President Putin said that people in the Transnistrian region of Moldova - which, like Ukraine, borders Russia, should have the right to decide their own fate. Read Paul Mason's blog from the area: Undercover in Transinstria, Russia's next potential flashpoint
He said Kiev needed to provide guarantees to its Russian-speaking population in the east of the country to resolve the crisis.
“The compromise must be found not between third party players but between the different political forces within Ukraine itself,” Mr Putin said. “This is extremely important, it is the key issue.”
Thursday’s talks brought the ministers of Russia, Ukraine and the United States together with the European Union’s foreign policy chief to discuss a crisis in which Kiev is struggling to reassert its authority in eastern towns largely controlled by armed pro-Russian separatists.
Upon arriving in Geneva on Wednesday, Ukrainian Foreign Minister Andrii Deshchytsia said there still is time for negotiations to ease tensions with Russia.
“I think that we still have a chance to de-escalate the situation using the diplomatic means,” he said. “And we will try hard. We are trying hard – not only Ukraine – but also the United States. However, the time is now, not only to express the concerns, but to look for a more concrete and adequate response to Russia’s plans and actions.”
The European Union said is it was willing to hold talks with Russia and Ukraine on gas security, it said in reply to a letter from Mr Putin in which he warned of gas supply disruption.
“We believe that this approach allows for the most useful process with the Russian Federation and other third parties,” European Commission President Jose Manuel Barroso said.