"I expect that there will be an announcement," White House Coordinator for Weapons of Mass Destruction Gary Samore told reporters.

"The negotiators have narrowed the differences, identified key issues and I think it will be possible for the presidents to have a good discussion, and hopefully reach agreement" on certain issues.

"There certainly won't be an agreement on the end deal... but I think you will see an announcement that indicates, you know, some progress toward reaching that objective," he said, referring to a deal by year's end.

Obama visits Russia Monday in the hope of finding agreements on military transit and weapons reductions to revive a relationship that last year plunged to a post-Cold War low.

Samore said plans to expand US missile defence - one of the issues behind frayed relations between Moscow and Washington - "would have to be addressed".

Russia is fiercely opposed to the missile defence project and has warned that the United States must address its concerns to move forward in the nuclear arms treaty negotiations.

Moscow views the system, which would see US missiles located in Poland and the Czech Republic, as a threat while Washington has sought to reassure Russia that the system is designed to defend against possible attacks from Iran.

"We don't believe it poses a threat to Russian strategic systems," Samore told reporters.

The president's visit was important both to honour the US vow to "reset" relations with Russia, and to win Moscow's backing on other issues, Samore went on.

"This new arms control treaty is important in terms of the reset of the US-Russian relations, and we think it will help gain greater cooperation from Russia on a number of issues including Iran and North Korea," he said.

A Russian news report said earlier that officials from both countries had yet to agree a framework document for replacing the Strategic Arms Reduction Treaty (START), which expires in December.

The signing of a declaration on a replacement for START has been expected to be a major outcome of the summit meeting between Obama and his Russian counterpart Dmitry Medvedev.

"I can confirm that the final agreement of the document has not been completed," a source in the Russian foreign ministry described as a high ranking diplomat told the Interfax news agency.

Issues still to be resolved included problems related to the parameters for reducing the number of carriers of nuclear warheads on both sides, the source was quoted as saying.

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