A man flying a mini helicopter illegally has landed his aircraft on the west lawn of the US Capitol, which houses Congress, triggering street closures around the building and prompting a police investigation.

"The US Capitol Police Hazardous Devices Section [bomb squad] is continuing to investigate the gyro copter," said Lieutenant Kimberly Schneider, a public information officer, on Wednesday.

Capitol Police did not immediately identify the pilot or comment on his motive, but a Florida postal carrier named Doug Hughes took responsibilty for the stunt on a website where he said he was delivering letters to all 535 members of Congress in order to draw attention to campaign finance corruption.

"As I have informed the authorities, I have no violent inclinations or intent," Hughes wrote on his website, thedemocracyclub.org.

"An ultralight aircraft poses no major physical threat - it may present a political threat to graft. I hope so. There's no need to worry - I'm just delivering the mail."

Michael McCaul, the House Homeland Security panel chairman, said the pilot landed on his own. He added that if he had landed the mini helicopter closer to the Capitol, authorities were prepared to shoot him down.

"Had it gotten any closer to the speaker's balcony they have long guns to take it down, but it didn't. It landed right in front," McCaul said.

Witnesses said the craft approached the Capitol from the west, flying low over the National Mall and the Capitol reflecting pool across the street from the building. It barely cleared a row of trees and a statue of General Ulysses Grant.

John Jewell, 72, a tourist, said the craft landed hard and bounced. An officer was already there with a gun drawn. "He didn't get out until police officers told him to get out. He had his hands up'" and was quickly led away by the police, Jewell said. "They snatched him pretty fast."

Downtown Washington is blanketed by restrictions on air traffic that generally prohibit aircraft from flying over the White House, the Capitol, the national Mall and key buildings without special permission.

Source: Agencies