* EU foreign ministers meet to discuss situation in Ukraine
* Emergency gathering to weigh response to Russia's seizure of Crimea
* Diplomats do not expect move on sanctions; mediation to be emphasised
* Germany, France, Finland promoting OSCE negotiation effort (Recasts with EU statement, adds details, quotes from Ashton)
By Justyna Pawlak and Luke Baker
BRUSSELS, March 3 (Reuters) - European Union foreign ministers held out the threat of sanctions against Russia on Monday if Moscow fails to withdraw its troops from Ukraine, while offering to mediate between the two, alongside other international bodies.
At talks on the Ukraine crisis in Brussels, they agreed no deadlines or details about any punitive measures that could be put in place against Russia, but leaders of the bloc's 28 nations will hold an emergency summit on Thursday and could take further decisions.
The EU discussions were convened abruptly after Russian President Vladimir Putin seized the Crimean peninsula and said he had the right to invade Ukraine.
"We need to see a return to barracks by those troops that have currently moved (from) where they have been staying," the EU's foreign policy chief Catherine Ashton told reporters after the foreign ministers' meeting in Brussels.
"There are serious concerns about overflights, about reports of troops and armed personnel moving."
In Monday's talks, EU governments sought to strike a balance between pressuring Moscow and finding a way to calm the situation.
"We want the situation to de-escalate to the position the troops had before this began," Ashton said.
Europe's approach leaves it at slight odds with the United States, after U.S. Secretary of State John Kerry threatened visa bans, asset freezes and trade restrictions against Russia, which he accused of 19th century behaviour in Ukraine.
Germany, France and Britain, the EU's most-powerful nations, were advocating mediation, possibly via the Organization for Security and Cooperation in Europe (OSCE), 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 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 Putin once described as the worst geopolitical catastrophe of the 20th century.
France's foreign minister, Laurent Fabius, said 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.
Radoslaw Sikorski, the foreign minister of Poland, a neighbour of Ukraine, took a harsher stance.
"The EU is saying that it will revise its relations with Russia if there is no de-escalation," he told reporters after the meeting.
One possible measure mentioned by the EU ministers after their meeting was a suspension of talks on visa issues with Russia.
"In the absence of de-escalating steps by Russia, the EU shall decide about consequences for bilateral relations between the EU and Russia, for instance suspending bilateral talks ... on visa matters ... and will consider further targeted measures," they said in a statement.
Russia and the European Union have been discussing visa cooperation since 2007, with Russia keen to have visa-free access to the EU's member states. It is an issue raised at nearly every meeting between Moscow and Brussels.
"Targeted measures means sanctions in normal language, visa and financial sanctions," Sikorski said.
Ministers also considered the possibility of imposing an arms embargo on Russia but after several hours of talks, no decision was taken on the issue after some governments expressed reservations.
Underlining the need for dialogue, German Chancellor Angela Merkel spoke to Putin late on Sunday and suggested a "fact-finding" mission to Ukraine, possibly led by the Vienna-based OSCE, currently chaired by Switzerland.
The OSCE said it was ready to play a role.
Speaking to Merkel by telephone on Sunday, U.S. President Barack Obama underscored the "complete illegitimacy" of Russia's actions. A senior U.S. official said Obama would make the same point to the leaders of Britain and Poland.
But many Europeans are concerned about pushing Putin too far, mindful of their 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.
Russia is the EU's biggest trading partner after the United States and China, with 123 billion euros ($170 billion) of goods exported there in 2012. It is also the EU's most important single energy supplier, 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. (Additional reporting by Robert-Jan Bartunek and Robin Emmott; Editing by Will Waterman, Giles Elgood and Philippa Fletcher)