Norway decided yesterday to stay on alert for possible radioactive pollution from the crippled Russian submarine, Kursk, despite Moscow's assurances that there were no leaks.
The Norwegian Defence Ministry said Moscow, which shares an Arctic border with Norway, had not asked Oslo for help.
"Data coming in now show that we can't see any sign of radioactivity," Mr Per Strand, acting head of the Norwegian Radiation Protection Authority, said after what he called "fairly intensive" tests of air and sea.
Norway has long feared radioactive pollution from its eastern neighbour. During the Cold War, the Soviet Union used the twin Arctic islands of Novaya Zemlya as a nuclear-testing ground. And the Russian Northern Fleet is based in Murmansk.
Meanwhile yesterday, the Pentagon said there was no indication that any US naval vessels were involved in the incident. A Russian admiral in Moscow told the ITAR-TASS news agency there were signs that the nuclear-powered Kursk was seriously damaged in a major collision, but gave no details.
"We have no indication that a US vessel was involved in this mishap," said Rear Admiral Craig Quigley, a Pentagon spokesman. He would not say if any US submarines were in the vicinity of the Kursk at the time of the incident.
He said a US surface vessel was in the general area "a long way away" from the Russian submarine. The Kursk had been taking part in a major air and sea exercise - the kind of event that would normally be followed closely by the US military.
Russian Admiral Vladimir Kuroyedor said the navy deployed all its rescue forces but "the chances of a favourable outcome are not very high".
Admiral Quigley said the Pentagon has received no request for help from the Russians. "I'm not sure what we could provide," he said.
The US navy has deep submersible rescue vehicles designed to remove crews from sunken US or NATO submarines. But, he said, "I don't believe they are adapted to get a seal on a Russian submarine."
The Russian navy has just one vessel still in service capable of rescuing the crew, a French naval expert said.