BRUSSELS (REUTERS) - European Union foreign ministers will push on Monday for high-level mediation to resolve the crisis over Russia's invasion of Crimea, while threatening the possibility of sanctions if Russia does not back down.

In emergency talks convened after Russian President Vladimir Putin seized the Crimean peninsula and said he had the right to invade Ukraine, ministers will try to strike a balance between pressure on Moscow and finding a way to calm the situation.

Germany, France and Britain, the EU's most-powerful nations, are all advocating mediation to resolve the crisis, possibly via the Organisation for Security and Cooperation in Europe, while not ruling out economic measures if Moscow does not cooperate.

"Crisis diplomacy is not a weakness but it will be more important than ever to not fall into the abyss of military escalation," German Foreign Minister Frank-Walter Steinmeier told reporters as he arrived for the talks in Brussels.

The seizure of Crimea has created the greatest confrontation between Russia and the West since the collapse of the Soviet Union in 1991, an event Mr Putin has described as the worst geopolitical catastrophe of the 20th century.

France's foreign minister, Laurent Fabius, took a similar line, saying France would be pushing on two fronts: "There's the condemnation of Russian intervention and then there's the need for mediation, for dialogue," he said.

A draft of the statement EU ministers will make, seen by Reuters, uses the phrase "strong condemnation" and calls on Russia to immediately withdraw its troops to base. Language on "targeted measures" against Russia remains in brackets, meaning it has not yet been agreed by all member states.

Underlining the need for dialogue, German Chancellor Angela Merkel spoke to Mr Putin late on Sunday and suggested a "fact-finding" mission to Ukraine, possibly led by the Vienna-based OSCE, currently chaired by Switzerland.

OSCE READY TO PLAY ITS ROLE

The OSCE said it was ready to play a role.

Europe's approach leaves it at slight odds with the United States, after US Secretary of State John Kerry threatened visa bans, asset freezes and trade restrictions against Russia, which he accused of 19th century behaviour in Ukraine.

"American businesses may well want to start thinking twice about whether they want to do business with a country that behaves like this," Mr Kerry said on Sunday.

European governments will take a more cautious approach, diplomats said, with any prospect of sanctions against Russia unlikely to be spelled out directly.

Several EU member states including Germany, France, Britain, the Netherlands and Finland are expected to push for mediation to calm the crisis, diplomats indicated. The OSCE said on Monday it was ready to play a role.

Speaking to Merkel by telephone on Sunday, US President Barack Obama underscored the "complete illegitimacy" of Russia's actions. A senior US official said Mr Obama would make the same point to the leaders of Britain and Poland.

But many Europeans are concerned about pushing Mr Putin too far, mindful of their deep economic links with Russia, including a heavy dependence on Moscow's gas and oil exports. There is also concern about the time required for sanctions and the legal hurdles that must be cleared.

European sanctions also require unanimity among the 28 member states, something that would be extremely difficult to achieve when it comes to Russia, with some small countries, such as Cyprus, having close ties to Moscow.

Moscow has said it is protecting the lives of Russian citizens and speakers in Ukraine, and appears to be calculating that the West cannot afford to risk a wider conflagration by taking anything approaching military action.

CLOSE RELATIONS

Russia is the EU's biggest trading partner after the United States and China, with 123 billion euros (S$215 billion) of goods exported there in 2012. It is also the EU's most important single supplier of energy products, accounting for more than a quarter of all EU consumption of oil and gas.

Relations between Brussels and Moscow have deteriorated over the last year, with EU governments expressing anger over Moscow's pressure on former Soviet republics hoping to forge closer economic ties with Europe, including Ukraine.

Tensions reached new heights when Moscow persuaded Ukrainian President Viktor Yanukovich to reject a trade deal with the EU in November, a decision that sparked three months of mass protests that ended with his overthrow.

One decision that could be agreed by EU foreign ministers is asset freezes against Ukrainians accused of misappropriating public funds, similar to measures taken by Austria, Switzerland and Lichtenstein last week.

Austria announced on Saturday that it was blocking the bank accounts of Yanukovich and 17 others, following a request by Ukraine's new authorities. Ukraine's new leaders have accused Yanukovich of embezzling as much as US$37 billion in three years.