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.
Mikser, who is to meet with NATO chief Anders Fogh Rasmussen in Brussels on Monday, added that talks are ongoing "about having NATO rotating land units in our region".
His Lithuanian counterpart Juozas Olekas said Friday 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 Friday.
- 'Concrete expectations' -
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 on Friday.
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.
"While we do not seek confrontation with Russia, its actions in Europe and Eurasia may require the United States to re-examine our force posture in Europe and our requirement for future deployments, exercises and training in the region," said Assistant Secretary of Defence Derek Chollet.
Speaking ahead of a NATO foreign ministers' meeting in Brussels earlier this month, Poland's top diplomat, Radoslaw Sikorski, said the country "would welcome any forces" on its territory.
"All members should enjoy the same level of security," he told reporters, after earlier saying he would be happy with two heavy NATO brigades at home.
His counterpart in Romania, which along with the Baltics joined the alliance in 2004, voiced concern Thursday over the developments in Ukraine, stressing that his country is "on the frontline".
"Romania has concrete expectations of a redeployment and an eastward repositioning of NATO's naval, air and ground forces," Foreign Minister Titus Corlatean told AFP.
"The Black Sea region must be a top priority for NATO and the EU," he said, calling on the alliance to take a firm stand to prevent a contagion of the Ukraine crisis.