Ex-Soviet countries fearing spillover from the Ukraine crisis have asked NATO for land forces and other backup, potentially moving the region one step closer to a new Cold War.
The nail-biting drama has already led the Western military alliance to step up defence measures in eastern and central Europe, but the region's leaders are seeking more.
The calls from Baltic states Estonia, Latvia and Lithuania -- which all border Russia and have sizeable ethnic Russian populations -- and Ukraine's neighbours Poland and Romania come as the United States accuses Russia of wanting to "create chaos" to have a pretext for more military intervention.
"We hope NATO's increased presence in the Baltic region is not just temporary and limited to reinforced air patrols," Estonian Defence Minister Sven Mikser said on state radio this week.
His Lithuanian counterpart Juozas Olekas said yesterday he was also in talks with the alliance on beefed-up security, with some decisions already made and others to be taken next week.
"The presence of NATO member forces in Lithuania may take various forms -- from instructors to permanently deployed land, naval, special operation or air forces," he told AFP.
NATO has already enhanced air policing over the Baltic states, deployed AWACS reconnaissance planes over Poland and Romania and overseen an increased naval presence in the Black Sea.
But Rasmussen himself said "we need to take more steps."
"These considerations might include an update and development of our defence plans, enhanced exercises and also appropriate deployments," he told reporters in Sofia on yesterday.
Poland's Jaroslaw Kaczynski, leader of the right-wing opposition, says he believes installing US military bases in his country would be the only way to counter Russian President Vladimir Putin's "expansionist ambitions".
The move would be highly controversial for Moscow, reversing an informal agreement made when NATO expanded east to include former Warsaw Pact countries that were eager to break away from years of Soviet domination.
"It's time to put an end to the restrictions on NATO troop presence in Poland," Kaczynski told reporters yesterday.
A senior Pentagon official had said Tuesday that Russia's takeover of Crimea could prompt a review of the US military presence in Europe, which has declined steadily since the end of the Cold War.