For Powell, Moscow is the last stop on a former-Soviet tour that first took him through the republics of Central Asia.

For the Russian leader, Powell's visit provides a chance to go eye-to-eye with the top US diplomat, reiterating his view that the size of nuclear arsenals should be governed not by verbal promises, as the US has suggested, but by formal treaties.

Russian Foreign Minister Igor Ivanov spoke of “unprecedented intensity at all levels" in diplomacy between the world’s biggest nuclear powers.

But agreement on the nuclear question is elusive, despite the warming relationship between US and Russian leaders.

The latest relevant treaty between the two is the Anti-Ballistic Missile Treaty, signed in 1972 by Richard Nixon and Leonid Brezhnev.

US President George W. Bush has called it “out of date.” But Putin has said that US plans to build a missile-defense shield, the so called “son of Star Wars”, will nullify the ABM Treaty and force negotiations on a new one.

The negotiations in Moscow regarding nuclear arsenals are part of the first major effort of this kind since the Soviet Union ended in 1991.

Last Wednesday, Russia and the US announced that they have slashed stockpiles of warheads to 5,518. But both have agreed in principle that their nuclear firepower still exceeds security demands of the day, and Bush has called for cuts down to levels last seen in the 1950s.

Powell was expected to fly to Berlin after his Russian visit.

Allies against terror

The US secretary's visit to Moscow also cements the countries shared “anti-terror” campaign, though the nuclear issue has dominated discussion.

He layed flowers at the site of an August 2000 bombing, at downtown Moscow’s Pushkin Square, where eight people died and scores more were injured.

“We have come together to combat this terrible scourge of terrorism and I am sure we shall be successful,” Powell said.

Russia, hit by a deadly series of bombings in 1999 and 2000, for which it blamed Chechen “terrorists” and “bandits”, had repeatedly warned Western countries of a threat linked to Osama bin Laden through Chechnya. More than 300 died in the blasts.

But the warnings often fell on deaf ears in the US intelligence community.

Since September 11, Russia’s warning has been taken more seriously, and Powell’s visit to Pushkin Square served as symbolic acknowledgement of this.

Despite many US diplomatic trips to Moscow since bombings there, there were no visits of commemoration until Monday’s – following a visit by Putin to “ground zero” in New York.

Odd couple

Yet the new rush to share intelligence and military resources in a common “war on terror” is an odd one.

No Russia-watchers doubt that the country is the victim of terror, but the nature of the attacks remains a subject of debate, as is Russia’s role in the battered breakaway republic of Chechnya.

Whereas US public opinion is firmly behind Bush’s anti-terror campaign, many Russians, especially Muscovites, are sceptical of American and Russian motives.

Their scepticism traces back to a bizarre event in September, 1999, when Russia itself was gripped with terror. Two apartment blocks had exploded in the middle of the night, each killing more than 100.

Deep in the night of September 22, police in the city of Ryazan arrested a group of men planting a device in the basement of another apartment building. The men turned out to be agents of the FSB, the Federal Security Bureau, successor to the Soviet secret police.

The bomb, according to official reports, was a “dummy”. What the police had believed to be explosives were just "packs of sugar."

Russians were told that the agents had merely been planting a fake bomb to test preparedness. But the country exploded with rumours that the real bombs may have been set by state agents, too, to terrorise the population and provide an opportunity for a surge in state power as Boris Yeltsin’s weak regime approached its end.

Such rumours persist today but appear to have been forgotten by Western diplomats, now developing robust relationships with Putin, himself a former secret agent with strong ties to the FSB.

It is the kind of conspiracy theory that can drive people mad, for lack of facts and excess of speculation. Putin has called it “delirious nonsense.”