There have been tense moments as Ukrainian and pro-Russian troops faced off in Crimea
A changing mood
60 secs: Armies comparedWatch
The Russian military says it has test-fired an intercontinental ballistic missile, as tension continues over Ukraine's Crimea region.
The planned test comes after the US accused Russia of deploying troops in Crimea in an "act of aggression".
Russian President Vladimir Putin denied doing so, but said he had not ruled out military action to protect Russians and Russian speakers in Ukraine.
US Secretary of State John Kerry accused Russia of seeking to invade.
The US is keen to label Russia's action an "invasion" but as yet no one has been shot by the troops, and it is still time for a war of words - on friend as well as foe, as it happens.”
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Growing war of words
Russia has strongly condemned the change of government in Ukraine, which came after months of street protests, more than 90 deaths and the flight of ousted President Viktor Yanukovych, a Russian ally.
Speaking during a visit to the Ukrainian capital Kiev, where he held talks with the new government, Mr Kerry said there was no indication at all that Russian citizens or Russian-speakers were in any danger in post-uprising Ukraine.
"It is clear that Russia has been working hard to create a pretext for being able to invade further," he said.
In one hint of progress on Tuesday, Ukraine's new Prime Minister Arseniy Yatsenyuk said consultations had taken place between Russian and Ukrainian ministers. He described them as "quite sluggish" but "first steps".
A Topol missile was in transit outside Moscow last week, Reuters reports
Russia's defence ministry said a Topol RS-12M missile had been successfully launched, from Russia's Kapustin Yar test range near the Caspian Sea to the Sary Shagan range in Kazakhstan.
"The aim of the launch was to test a promising intercontinental ballistic missile payload," it said, adding that the nuclear-capable missile reached its target successfully.
It is what the international community fears most: a confrontation that spills out of control and leads to war”
Christian FraserBBC News, Sevastopol
Resistance proves problem for Russia
The US said it was given advance notice of the missile launch, as required by bilateral arms treaties.
The BBC's diplomatic correspondent Jonathan Marcus says such tests are planned long in advance, but that it inevitably adds another element of Cold War-style tension to the current crisis.
Moscow is in de facto control of the Crimean peninsula after troops thought to be Russian or pro-Russian began taking control of strategic points on Saturday.
US Secretary of State John Kerry: "The US will stand with the Ukrainian people"
21 February - After months of protests, President Viktor Yanukovych signs a deal with opposition leaders to reduce his powers and hold early elections
22 February - Mr Yanukovych goes missing; protesters walk unopposed into official buildings as police abandon posts; parliament votes to impeach the president and calls elections for 25 May
23-26 February - Parliament names speaker Olexander Turchynov as interim president and Arseniy Yatsenyuk as PM; an arrest warrant is issued for Mr Yanukovych, who alleges a coup
27-28 February - Pro-Russian gunmen seize key buildings in Crimean capital, Simferopol
1 March - Russia's parliament approves the use of military force; armed men blockade Ukrainian bases in Crimea
4 March - Russian President Putin denies troop deployments; US Secretary of State John Kerry condemns Russian "act of aggression"; Russia test-fires a ballistic missile
Ukraine crisis timeline
Russia's trade ties with Europe
Does Russia have a case?
Troops are surrounding Ukrainian military bases and other installations, while two Ukrainian warships are reported to be blocked by a Russian ship in the port of Sevastopol.
Ukrainian TV reported on Tuesday evening that armed men had attempted to take over an anti-aircraft missile base in Yevpatoria, on the coast north of Sevastopol.
Kiev and the West have alleged Russia is mounting an invasion of Crimea, which has a majority Russian-speaking population.
US President Barack Obama accused Russia of "seeking through force to exert influence on a neighbouring country".
"That is not how international law is supposed to operate," he said.
But at a lengthy news conference on Tuesday, in his first public comments on the issue, Mr Putin denied the heavily armed troops were Russian. He said they were "local self-defence forces" loyal to Moscow, protecting the bases from "nationalists" and "anti-Semites".
Russia, said Mr Putin, reserved the right to act to protect Russian citizens and speakers anywhere in Ukraine.
In Crimea and in eastern Ukraine, there have been shows of support for Russian intervention.
Pro-Russian troops have blocked Ukrainian soldiers in their barracks in Crimea
Russian President Vladimir Putin denies having deployed any troops in Crimea and says the soldiers are self-defence groups
But on Tuesday a peace rally in the eastern city of Donetsk urged Russia to stay away.
"We did not ask for help. I don't want him, Putin, to bring tanks here. I don't want them to shoot at my kids," one woman, Natalia Sytnik, told Reuters.
"Let him hear us: 'Do not defend me from anyone. No-one is attacking me'."
In other developments on Tuesday
Nato and Russia agreed to hold talks on Wednesday. Nato Secretary General Anders Fogh Rasmussen said Russia continued to "violate Ukraine's sovereignty and territorial integrity", presenting "serious implications for the security and stability of the Euro-Atlantic area"
EU foreign policy chief Catherine Ashton had "a useful discussion" with Russian Foreign Minister Sergei Lavrov in Madrid, said an EU source
Mr Lavrov said the Russian position was "honest" and would not change, and that sanctions against Russia would be "counter-productive"
A court in Kiev quashed the decision by Crimea's parliament to sack the region's government and also ruled that the move to hold a local referendum on Crimea's status was illegal
Both the US and the EU have offered financial help to Ukraine, which is facing a growing economic crisis amid its severed ties with Moscow.
Mr Kerry took to Kiev a $1bn (£600m; 720m euros) package of energy subsidies, and told the crowds who remain in Independence Square after months of protests that President Obama "is planning more assistance".
The EU is considering paying the $2bn which Ukraine owes to Russia in gas bills, said EU Energy Commissioner Guenther Oettinger.