MOSCOW (AFP) - The air forces of Russia and the United States engaged in a diplomatic dogfight Friday over a commemorative flight using a nuclear bomber, a plan that Moscow said was shot down by Washington.

Russia had earlier announced it would for the first time land a Tu-95 nuclear bomber (right) on US territory as it celebrated the 100 year anniversary of the birth of Valery Chkalov -- who took a non-stop flight over the Arctic and landed in the US state of Washington in 1937.

But Russia's air force chief announced Friday that US authorities did not appear to trust Moscow's intentions and demanded that a US pilot be placed in the bomber to oversee the flight.

"These conditions are unacceptable," air force chief Vladimir Mikhailov said in televised remarks.

But US officials in Moscow said they were perplexed by Mikhailov's remarks.

"We never put any restrictions on them," a US official here told the ITAR-TASS news agency.

The official said that Americans offer the assistance of a US pilot "to crews that are unfamiliar with the terrain, the language and other issues. But this is not a requirement -- it is an offer."

The spat marred what was otherwise supposed to be a festive occasion marking a new post-Cold War friendship between Moscow and Washington.

The nuclear bomber was supposed to cover a similar route to the plane piloted by Chkalov and mark the first time that a Russian bomber -- even without its weapons -- landed on US territory.

The Tu-95 was considered as one of the most effective intercontinental nuclear bombers and is still used by Russia's armed forces after first being developed by the Soviet Union in the 1950s.

It is occasionally used by the Russian armed forces in war games staged over the Atlantic and its flight was -- according to officials here -- supposed to represent a rapprochement between Moscow and Washington following the September 11 attacks.

Chkalov (pictured at right) -- who had tense ties with Soviet dictator Stalin -- died in a mysterious air crash a year after his historic flight.

His Antonov-25 plane that he flew over the Arctic in 1937 is pictured below.