Britain warned Russia on Sunday against intervening in Ukraine's "complex" crisis, saying London wanted to contribute to an international economic program aimed at shoring up the "desperately difficult" situation of the Ukrainian economy.

Also on Sunday, Ukrainian parliament voted to appoint Oleksandr Turchinov, the closest confidante of freed opposition leader Yulia Tymoshenko, the role of president following Sunday's ouster of Victor Yanukovych.

Ukraine's parliamentary speaker and newly appointed interim president told deputies to agree on the formation of a national unity government by Tuesday. "This is a priority task," Turchinov said.

In comments that may anger Moscow, British Foreign Secretary William Hague said his government was in regular contact with the Russian government to try to persuade it that closer ties between Ukraine and the European Union should not worry it.

"If there's an economic package, it will be important that Russia doesn't do anything to undermine that economic package and is working in cooperation and support of it," Hague told BBC TV.

When asked if he was worried that Russia might "send in the tanks" to defend the interests of Russian-speakers in eastern Ukraine, Hague warned against what he called "external duress" or Russian intervention.

"It would really not be in the interests of Russia to do any such thing. We have to keep up the communication with Russia as we are doing ... so that the people of Ukraine can choose their own way forward. There are many dangers and uncertainties."

Ukraine's parliament voted to remove President Viktor Yanukovych on Saturday after three months of street protests, while his arch-rival Yulia Tymoshenko hailed opposition demonstrators as "heroes" in an emotional speech in Kiev after she was released from jail.

The crisis began as protests against Yanukovych's decision to abandon a trade agreement with the European Union in favor of closer ties with Russia, which promised to lend Ukraine $15 billion euros. Ukraine needs the money -- foreign investment inflows fell by almost half last year, to a net $2.86 billion from $4.13 billion in 2012

Britain has so far assumed a lower profile on Ukraine than countries such as Germany and Poland, though Prime Minister David Cameron spoke to Russian President Vladimir Putin last Thursday about the situation there and Hague said he'd be talking to Russian Foreign Minister Sergei Lavrov on Monday.

Hague said the priority was to persuade Moscow that the fate of Ukraine - a country that was part of the Soviet Union and has been within Russia's sphere of influence for decades - was not what he called "a zero-sum game" and that closer ties with the EU were not a bad thing.

"It's in the interests of the people of Ukraine to be able to trade more freely with the EU. It's the interests of the people of Russia for that to happen as well."

He said he didn't know what Russia's "next reaction" would be, but he pushed the Ukrainian opposition to move urgently to form a government of national unity, agree arrangements for new elections, and to crack on with shoring up the economy.

"While all this has been happening, the Ukrainian economy is in a desperately difficult situation," Hague said. "And they need an economic program that the rest of us, through the International Monetary Fund and other institutions, can support so that they can stave of an even more serious economic situation."