There's been a second high-level telephone conversation in twenty-four hours between the United States and Russia as attempts continue to resolve the crisis in the Ukrainian region of Crimea.
The Russian foreign minister, Sergei Lavrov advised his American counterpart John Kerry not to take hasty actions that could harm bilateral relations, and warned that sanctions could backfire.
Washington now says it believes twenty-thousand Russian troops are in Crimea, where tensions remain high.
At one stage, armed men briefly surrounded a Ukrainian missile defence site.
Russia has urged the United States not to take any steps that could harm relations between the two.
Russia has urged the United States not to take any steps that could harm relations between the two.
Earlier, the upper house of the Russian parliament offered its support to Crimean plans to join Russia.
But Ukraine's prime minister has warned the Crimean parliament that "no-one in the civilised world" will recognise its referendum on joining Russia.
Ukrainians carrying their country's flags stage a protest at the Chongar check point blocking the entrance to Crimea. Photo: AFP
Arseniy Yatsenyuk and others in the Kiev government have called the vote "unconstitutional" and "illegitimate".
Mr Yatsenyuk says the country is ready for talks with Russia, but Moscow must first withdraw its troops, abide by international agreements and halt its support for what he called separatists and terrorists, the BBC reports.
He says he's requested a second telephone call with Russian prime minister Dmitry Medvedev to discuss the matter.
Crimea's pro-Moscow leadership, which took power when Russian troops seized the region last week, is organising an urgent referendum on whether to join Russia.
It is expected the majority Russian-speaking population in the Ukrainian territory will endorse joining Russia.
The referendum has the support of the Russian parliament.
The speaker of the Russian upper house said if the Crimean people vote on 16 March to join Russia then they would "unquestionably back this choice".
The decision by Crimean MPs to seek to join the Russian Federation comes amid international tensions over the presence of pro-Russian troops in the southern Ukrainian peninsula.
Kiev does not recognise Crimea's pro-Moscow leadership, which was sworn in at an emergency session as pro-Russian forces began to take over strategic sites last week.
Crimea's leadership for its part has branded as "illegitimate" the interim government in Kiev, which was sworn in at the end of February after the ousting of President Viktor Yanukovych.
Meanwhile, Ukraine's Paralympic team has confirmed it will take part in the Sochi Winter Paralympics.
The head of the team, Valeriy Sushkevych, said they would participate, but warned: "If something major happens, Ukraine will leave the Games immediately".
China called for calm and restraint in the Ukraine crisis on Saturday, saying that the issue should be resolved through talks and political means.
Foreign Minister Wang Yi urged all parties to keep in mind the fundamental interests of all ethnic communities in Ukraine and interests of regional peace and stability.