Brussels - Nato will deploy more aeroplanes, ships and military staff to eastern member states in response to the unrest in Ukraine, as a military standoff intensified Wednesday between pro-Russian militants and Ukrainian troops in the east.
Nato Secretary General Anders Fogh Rasmussen said: "We will have more planes in the air, more ships on the water and more readiness on the land."
The alliance's eastern-most member states have said they feel threatened by Russia, which has annexed the Ukrainian Black Sea peninsula of Crimea.
Western nations have accused Moscow of applying military pressure on Ukraine and instigating protests in the country.
"Russia is exporting not just oil and gas, but also terror to Ukraine," Ukraine's acting prime minister, Arseniy Yatsekyuk, said, calling on Moscow to withdraw its "spy and sabotage groups".
Rasmussen said Nato still hoped for a political solution, pointing to talks Thursday between Russia, Ukraine, the United States and the European Union in Geneva.
A spokesperson for German Chancellor Angela Merkel expressed hope that the discussions will offer "a first step to restore an orderly situation in Ukraine".
Russia criticises US
But hours before the Geneva meeting, the Russian Foreign Ministry criticised the US for approving a "war that Kiev has declared against its own people", by justifying Kiev's military intervention against pro-Russian separatists in the east.
Accusing the US of double standards, it charged that Washington defended the overthrow of the legitimate government in Kiev as a popular uprising, but has criticized the protests in eastern Ukraine as terrorism.
The ministry was referring to the government of president Viktor Yanukovych who was ousted in late February. The former ruling Party of Regions has called on the pro-Russian militants in the east to give up their arms and vacate occupied government buildings.
The resolution was declared to have been passed unanimously although a number of delegates voiced opposition, the Interfax Ukraine news agency reported, by the party's Donetsk region branch.
It warned against the country's break up and called for the devolution of central powers to the regions to save a unified Ukraine.
Yanukovych hails from the Donetsk region. The party distanced itself from him after his ouster, but remains the country's most pro-Russian political force.
Meanwhile, the government in Kiev has launched an "anti-terrorist" operation to root out pro-Russian separatists in the east, despite warnings by Moscow that such actions would undermine the Geneva talks.
Video footage posted on espreso.tv showed that a Ukrainian army formation in the eastern city of Kramatorsk had defected to join the Russian separatists.
The video showed the formation - which included at least 10 armoured tanks - driving through the city bearing Russian flags.
Unknown activists, thought to be pro-Russian, seized the city council in Donetsk, bringing the number of occupied buildings in the industrial city to two. A dpa reporter saw masked men inside the building, but couldn't gain access inside.
The Ukrainian flag was still flying over the building. The Russian separatists also for the first time claim to have acquired Armoured Personnel Carriers, which they captured from Ukrainian paratroopers.
"Now the Donetsk 'People's Republic' has its own army, has its own paratroopers," said Miroslav Rudenko, a leader within the pro-Russian movement. The Ukrainian Defence Ministry said Russian "terror commandos" and local extremists had seized a number of paratroopers in Kramatorsk.
The armoured vehicles were later seen in the centre of Sloviansk city together with armed men "who have nothing to do with the Ukrainian armed forces," the ministry said.
In Brussels, Rasmussen said the alliance's ambassadors have agreed to fly more sorties for an air policing mission over the Baltic states, send ships to the Baltic Sea and eastern Mediterranean, and deploy military staff.
Nato's top commander in Europe, General Philip Breedlove, said the new measures would be in place until at least 31 December, with longer-term initiatives to be considered at a later stage.
Breedlove said he was planning to submit a list of the new deployments and did not rule out that ground forces could eventually be part of the mix.
"These measures are not a threat to Russia," he said. "The measures adopted today are defensive in nature and designed to reassure our allies in the east of our unshakable commitment to our collective defense responsibilities."
The German Defence Ministry said it would contribute a supply vessel and a set of patrol flights to Nato's military buildup in the east.
The Elbe, a lightly armed German Navy supply ship with a crew of 45, would act as mother ship for a Nato mine-clearing exercise in the Baltic Sea starting at the end of May, a spokesperson said.
From September, up to six German Air Force Eurofighter jets would be available for up to four months of Nato patrol flights over the Baltic region.
Nato plans to deploy 10 jets at a time for the patrols. The Geneva talks are expected to be decisive in determining whether further measures are imposed.
Some European countries are reluctant to proceed with economic sanctions because of their links to Russia, which supplies a large share of European energy.