Nato has announced it is to bolster its presence in eastern Europe in response to the crisis in Ukraine as preparations began for RAF jets to be sent to the region.
The alliance's secretary general, Anders Fogh Rasmussen, promised "more planes in the air, more ships on the water, and more readiness on the land" to reassure eastern European Nato members concerned about Russia's intentions.
Defence secretary Philip Hammond had already offered Typhoon aircraft to support the air policing effort in the Baltic and the Ministry of Defence confirmed preparations had begun for their deployment to Lithuania.
Ukrainian armoured vehicles blockaded by locals in Kramatorsk
Following a meeting of the North Atlantic Council in Brussels, Mr Rasmussen said Moscow must make clear "it doesn't support the violent actions of well-armed militias or pro-Russian separatists" in eastern Ukraine.
Setting out the extra steps Nato would take, Mr Rasmussen said aircraft involved in the air policing mission would "fly more sorties over the Baltic region".
He added: "Allied ships will deploy to the Baltic Sea, the Eastern Mediterranean and elsewhere, as required. Military staff from allied nations will deploy to enhance our preparedness, training and exercises. Our defence plans will be reviewed and reinforced."
The news comes after reports from the Ukraine defence ministry that pro-Russian militants had seized six Ukrainian armoured vehicles in the east of the country.
Reports coming out of the city of Kramatorsk said the occupants of the vehicles were disarmed following a blockade by locals.
According to the defence ministry "a column was blocked by a crowd of local people in Kramatorsk with members of a Russian diversionary-terrorist group among them," the BBC reported.
Meanwhile, pro-Russian militants are reported to be in control of Slaviansk, a town north of Kramatorsk, according to CNN, which reported that the atmosphere appears more relaxed than in recent days with locals welcoming pro-Russian forces.
Reuters said these latest military setbacks have left the Ukraine government looking weak on the eve of a peace conference in Geneva on Thursday, when its foreign minister will meet counterparts from Russia, USA and Europe.
No further British forces are expected to be committed to eastern Europe as a result of the Nato announcement, but a Ministry of Defence spokesman said the RAF was sending logistical support equipment for the Typhoons to the region ahead of the deployment of the jets to Siauliai in Lithuania.
"Some logistical equipment is going out to support the deployment when that does happen," a spokesman said.
A Ukrainian Army soldier speaks with local residents from Kramatorsk
When he announced the deployment last month Mr Hammond said the fighter jets would be available from late April to bolster the Polish contribution to the routine Nato defensive operations over Estonia, Latvia and Lithuania.
With the Geneva talks high on politicians' minds, foreign secretary William Hague warned Moscow it is in danger of making a "grave miscalculation" in the crisis sparked by the overthrow of president Viktor Yanukovych in February.
Mr Hague said in his annual Mansion House speech in the City of London: "In recent days Russia has deliberately pushed Ukraine to the brink, and created a still greater risk of violent confrontation. We call on Russia to stop these actions and to condemn the lawless acts in eastern Ukraine.
"Russia must choose whether it is open to diplomacy and de-escalation, and if it decides otherwise, we must be ready for a different state of relations with Russia in the next 10 years than in the last 20.
"My message to Moscow is that if anyone thinks they can do these things without serious long-term consequences they are making a grave miscalculation."
Mr Hague's words were backed by US support with a senior official saying that President Barack Obama had laid the responsibility of calming the crisis firmly at Moscow's door.
President Vladimir Putin is expected to give an indication of how far he is prepared to go in Ukraine when he attends an annual question and answer session with Russian citizens on Thursday.