U.S. embassies in Finland and Latvia issued a rare warning to Americans in the Nordic and Baltic region to be wary of shopping centers and public transport amid a threat of a possible terror attack Monday.

The new warnings came ahead of Tuesday's U.S. elections, and some officials said the alert may be linked to the vote.

Norway closed its embassy in the Latvian capital of Riga after receiving "concrete information," Norwegian Prime Minister Kjell Magne Bondevik (search) said without elaborating.

Latvia's security service said Saturday that it had received intelligence reports from Norway, Estonia and the United States of a possible terrorist strike against the small Baltic country.

Latvia (search), along with the neighboring Baltic nations of Estonia (search) and Lithuania (search), have been staunch supporters of the U.S.-led invasion of Iraq, and have a combined total of more than 200 soldiers there. Denmark has 501 soldiers in Iraq. Finland, Norway and Sweden did not support the invasion.

The U.S. Embassy in Riga warned on its Web site that U.S. citizens should "avoid large shopping areas and transportation hubs on or about Nov. 1, 2004."

An alert posted late Saturday on the Web site of the U.S. Embassy in Helsinki urged "all U.S. citizens in the Nordic and Baltic countries to be vigilant as to their surroundings, especially in centers of ground-based mass transit." It also said they should report anything suspicious to police.

U.S. embassies in Denmark, Norway and Sweden did not issue warnings.

Victoria Middleton, an embassy spokeswoman in Helsinki, said Monday the information was as specific as possible at this time.

"If we had more specific information for American citizens, we would of course release it," she said.

The Norwegian prime minister declined to give details on the threat that led to its embassy closure in Riga.

"I do not want to say what kind of information or by whom," Bondevik told reporters at a meeting of Nordic premiers in Stockholm, Sweden.

Finnish Prime Minister Matti Vanhanen said he had heard about the threat Friday and had been in touch with officials in the Baltic states.

"The authorities take this seriously because Monday, Nov. 1, has been mentioned as a possible date for terrorist actions," Vanhanen said.

Finnish police said security increased at the U.S. Embassy in Helsinki, but reassured Nordic citizens they had nothing to worry about.

"The United States has a lower threshold when it comes to warning its citizens, but we have no concrete information that would warrant such a warning," said Paavo Selin, head of Finland's counterterrorism unit.

"Because the U.S. elections are so close, this could be tied to that," Selin said.

Swedish Prime Minister Goran Persson (search) said his country had been warned about the threat. But he said there was no need to change security arrangements.

"We have a preparedness which we think is high, and this information does not change the way we act," Persson said at a joint news conference with his Nordic counterparts.

Usama bin Laden mentioned Sweden in his latest videotape — noting that he had never attacked the country. The message contained no threats against Sweden.