Russia is unclear about Washington's offer on the U.S.-Europe missile defence and soon will give a response to plans for deployment of interceptor missiles in the region, President Dmitry Medvedev said on Sunday.

The United States has invited Russia to monitor, using its own radars, the performance of U.S. interceptor missiles being deployed to shield Europe from attacks by countries such as Iran.

Russia maintains that the U.S. system threatens to neutralise its nuclear potential and seeks legally binding guarantees that Washington's interceptor missiles will not undermine its security.

Unfortunately, there are no agreements now and we do not quite understand what our partners are offering us, Medvedev said at a news conference after the APEC summit in Honolulu.

I think that in the nearest future we will give expanded assessment of how Russia will react to the developments concerning missile defence, both currently and after (its second phase launch) in 2015, he said.

Russia has long threatened a new arms race if the United States turns a deaf ear to its concern and goes ahead with its anti-missile system, to be deployed in four phases. The second phase in Romania will be operational in 2015, and the full system is due to be in place by 2020.

U.S. President Barack Obama improved relations with Russia as part of a reset policy, scaling down his predecessor's plans for missile defence in central Europe, but Russia says the revised system still threatens to weaken its nuclear potential.

Despite Russia's request, Washington said it will not be able to provide legally binding guarantees on its missile defence system for Russia, because they would require approval by Congress, which is critical of any limits on U.S. anti-missile architecture.

Failure to agree on cooperation in coming months would foster mistrust between ex-Cold War era foes ahead of the likely return of Prime Minister Vladimir Putin, a long standing critic of the West, to the presidency after March election and the U.S. presidential vote in November. (Reporting By Alexei Anishchuk; Editing by Robert Birsel)