Russian Prime Minister Dmitry Medvedev slammed as "unacceptable" the recognition and support by France and other states of the Syrian opposition battling the regime of President Bashar al-Assad.

In a wide-ranging interview with Agence France-Presse and Le Figaro ahead of a visit to Paris starting Monday, Medvedev also spoke of the EU economic crisis as a "serious threat" and did not rule out returning to the Kremlin in the future.

France was the first Western state to recognise the newly-formed Syrian National Coalition as the sole representative of the Syrian people and was swiftly joined by Britain. Paris has also suggested arming opposition fighters.

"From the point of view of international law, this is absolutely unacceptable," Medvedev said in the interview at his suburban Gorki residence.

"A desire to change the political regime of another state by recognising a political force as the sole carrier of sovereignty seems to me to be not completely civilised," he added.

The EU, Italy as well as Turkey and the Gulf Cooperation Council have also recognised the National Coalition as legitimate representatives of the Syrian people.

"Let the Syrian people decide the personal fate of Assad and his regime," Medvedev commented.

Moscow has been sharply criticised abroad for not abandoning the Syrian regime. But Medvedev said: "Russia does not support the Assad regime or the opposition. We have a neutral position."

He defended Russian military cooperation with Syria, saying "all we have delivered are arms for defence against external aggression".

Medvedev said above all Moscow was concerned that the conflict did not cause Syria to split into pieces. "As this will be used by religious extremists. And this is in no country's interest."

Medvedev said Moscow was nervously watching the economic crisis in the European Union, which he said seriously threatened Russia's own economic performance.

"We see this as a very serious threat," Medvedev said. "We are to a large extent dependent on what happens in the economies of the EU."

Medvedev noted that EU states account for half of Russia's trade volume while Moscow holds some 41 percent of its foreign currency reserves in euros.

"We are watching nervously. Sometimes it seems our European partners lack the energy and will to take decisions. And there is that endless dispute of what is better, fiscal consolidation or development," Medvedev said.

"It seems our European partners are moving towards an agreement but the main thing is that it is not late," he added.

Medvedev said Russia is paying particular attention to what he described as the "weak links" in the eurozone such as Greece and Spain.

But he emphasised that Russia has no intention of moving out of euros in its reserves even though he acknowledged bringing up the importance of the currency in conversations with EU leaders.

Medvedev said he is not ruling out a return to the Kremlin after his 2008-12 single term as Russian head of state but was happy working as premier under his mentor President Vladimir Putin.

"If I have sufficient strength and health, if our people trust me in the future with such a position, then of course I do not rule out such a turn of events."

"Never say never, especially as I swam in that river once and this is a river that you can swim in twice," he said.

Medvedev served as president after Putin stepped aside following the maximum two consecutive terms allowed by the constitution after his 2000-08 stint.

But Putin, 60, stayed on as a powerful prime minister and Medvedev, 47, never fully emerged from the shadow of his fellow Saint Petersburg native, an impression reinforced when Putin returned to the Kremlin in May 2012.

Medvedev played up the tight links between the two men, saying: "I would hardly have become prime minister under another president. I cannot imagine it at all."

Medvedev has taken his distance from Putin however on some issues, notably the case of feminist punk rockers Pussy Riot, two of whom have been sent to prison camps for performing a song against the Russian strongman in a church.

Reaffirming his belief they should be released, he said: "I think they have already tasted what prison is... So further punishment in the form of prison is not necessary. This is my personal position."