Four U.S. lawmakers arrive in Toronto tomorrow to learn how Canadian authorities thwarted an alleged terrorist plot last month.

But the visit is so shrouded in secrecy that the politicians will not discuss details of it until they are safely back stateside on Tuesday.

The members of the House Homeland Security Subcommittee on Intelligence, Information Sharing and Terrorism Risk Assessment will be on a fact-finding tour.

"I look forward to reviewing exactly how Canadian authorities were able to successfully share information throughout their law enforcement agencies and then use that intelligence to uncover and terminate the planned terrorist attack," Representative Jim Gibbons, a Republican from Nevada, said in a statement yesterday.

"By fostering partnerships and sharing information between U.S. and Canadian law enforcement agencies, I am confident that the security of both countries drastically increases."

On June 2, 17 suspects were arrested as part of what police called a "homegrown" terrorist cell allegedly plotting attacks in southern Ontario.

Police have said seven members of the group sought to acquire three tonnes of ammonium nitrate to bomb CSIS's downtown Toronto headquarters, near the CN Tower.

`Members of the House Homeland Security Committee can learn a lot from our neighbours'

Rob Simmons, Republican congressman

The subcommittee is chaired by Rob Simmons, a Connecticut Republican congressman, and also includes Democrats Zoe Lofgren of California and Donna Christensen of the U.S. Virgin Islands.

They apparently have a busy agenda in Toronto.

"The members of Congress will likely meet with local law enforcement officials, the Royal Canadian Mounted Police, the Canadian Security Intelligence Service as well as local Muslim leaders," said the subcommittee's website.

"Members of the House Homeland Security Committee can learn a lot from our neighbours to the north about these homegrown extremist groups and how the Canadian government was able to uncover and interrupt the plot," Simmons said in a statement.

Provincial government sources say the Americans will be given a "technical briefing" by Ontario Provincial Police deputy commissioner John Carson and other OPP officials specializing in anti-terrorism efforts.

John Goodwin, an aide to Simmons, confirmed the delegation will speak with reporters only upon their return to Washington, he said.

Goodwin, who declined to say which Muslim leaders would be meeting with the politicians, said the "sensitive nature" of the mission was reason for the precautions.

Sources say the Muslim Canadian Congress was not invited to meet with the Americans. Instead, the lawmakers will have talks here with U.S.-based Islamic groups that have local offices.