Nato has opened its first military mission in Russia, the day before a summit meeting in Rome which will give Moscow a limited say in the alliance's decision making.

On Tuesday, President Vladimir Putin will sign an agreement that will establish a Nato-Russia council, concluding an agreement struck earlier this month in the Icelandic capital, Reykjavik.

"This is a big change - because it will allow Nato countries and Russia to discuss and take decisions on things to be done in co-operation in many fields of security and military interest," said Admiral Guido Venturoni, the head of Nato's military committee, as he inaugurated the mission.

But just as the office was opened, Russia proved that its new status did not mean it would agree with Nato on all issues - restating its firm opposition to the alliance's eastward expansion.

Get-out clause

The council, which will meet every month, has been hailed as a fresh beginning in the relationship between Russia and Nato, putting the country on an equal footing with Nato's existing members for the first time.

From our point of view, enlargement provides nobody - not Nato itself and not its new members - with additional security

Alexander Yakovenko Foreign Ministry spokesman

It replaces a consultative body set up five years ago, consistently viewed as unsatisfactory by the Russians because it involved their diplomats only after Nato members had negotiated their own consensus.

Under the new arrangement, Russia will be consulted from the outset. But, at least for the moment, participation is limited to issues like the war on terrorism, non-proliferation and sea rescue.

The two sides will only decide on issues where they can find consensus. There is a clause that allows Nato members to withdraw any contentious issues from the agenda and discuss them among themselves.

The further expansion of Nato into the former eastern bloc is one issue already known to cause serious hostility from Russia.

"We unequivocally see it as a mistake," said a foreign ministry spokesman Alexander Yakovenko said, as quoted by the RIA Novosti news agency. "From our point of view, enlargement provides nobody - not Nato itself and not its new members - with additional security."

"From whom is Nato preparing to defend its new members? And why is such a defence needed if we are no longer enemies and the period of confrontation is over?"

The BBC's Nikolai Gorshkov in Moscow says Moscow fears eastward expansion will tip the balance of conventional forces in Europe, and jeopardize its hard earned position in the new Russia-Nato council.