WASHINGTON (Reuters) - U.S. officials have been working with Canadian authorities on security for the Winter Olympic Games next month in Vancouver but no unusual threats have emerged so far, U.S. Homeland Security Secretary Janet Napolitano said on Tuesday.

The Olympics open on February 12 and are expected to draw some 5,000 athletes, 10,000 members of the media and tens of thousands of spectators, a scene that could present an inviting target for an attack.

"We have been working with the Canadians all year long on the security of the Olympics," Napolitano told reporters. "We have a joint command center at the border; we have also taken other measures."

Asked if there were any special concerns about the threat picture for the games, Napolitano said: "No."

The Olympic Games have a C$900 million ($851.4 million) security budget which is mostly being funded by the Canadian federal government. Vancouver is about 30 miles from the U.S. border.

There will be more than 15,000 police, troops and private security guards at the games and the U.S. State Department has advised Americans to exercise caution, particularly at venues not associated with the Olympics like hotels and transportation systems.

"While there have been no specific, credible terrorist threats to the Vancouver 2010 Olympic Games, in the post-September 11th world, the threat from international terrorist groups at major public events is always a principal concern," the State Department's security assessment said.

It noted that al Qaeda has in the past succeeded in attacking major hotels, embassies and large office buildings which "makes it one of the greatest potential threats to the Olympics."

(Reporting by Jeremy Pelofsky, editing by Cynthia Osterman)