NATO Secretary General George Robertson said Monday that the NATO-Russia relationship has proved "durable and strong enough to overcome periods of disagreement."

He made the statement when commenting on Acting Russian President Vladimir Putin's remarks during his interview Sunday with the British Broadcast Corporation.

The NATO chief welcomed "the positive spirit" shown by Putin on the BBC program, saying NATO recognizes "the need for partnership between the Alliance and Russia, and will work hard to build on our existing links."

Robertson said NATO's effort makes for an already challenging task, but said Russian membership of NATO is not on agenda at present.

Putin's comments underline "the renewal of our partnership, as did my recent visit to Moscow," Robertson said.

In another development, Russian Foreign Minister Igor Ivanov said on the same day that Putin's statement dose not rule out joining NATO and it is "a hypothetical answer to a hypothetical question."

Putin "set out Russia's fundamental principles for its relations with the North Atlantic alliance, which means that we are ready for and interested in being NATO's partner in dealing

with key modern problems, and primarily in creating a new architecture of European security," Ivanov said.

Russia froze its ties with NATO last March when the military bloc started air strikes against Yugoslavia. Their relations thawed last month with Robertson's visit to Moscow. But mistrust

persists in the relationship as Russia remains adamantly opposed to NATO's further expansion eastward. Brussels' criticism of Russia's military actions against rebels in its breakaway republic of Chechnya has also strained their ties.