WASHINGTON, Aug 8 (Reuters) - Further tightening security ahead of the first anniversary of the Sept. 11 attacks on the United States, the Secret Service has banned truck traffic on Washington's 17th Street along the White House complex.

Street signs on Thursday announced the ban along an eight-block stretch and authorities confirmed the Secret Service was imposing it from Friday to guard against potential truck bombs.

The agency also barred unauthorized vehicles from parking on a four-block section of 17th Street along the Eisenhower Executive Office Building, which is next to the White House inside the executive complex.

Authorities described the measures as a "regular enhancement" to security and said they were not in response to a specific threat or linked to the Sept. 11 anniversary.

Parking and traffic restrictions around the White House have expanded over the years in response to threats or violent incidents. Pennsylvania Avenue on the north side of the White House was closed to all vehicle traffic after the 1995 Oklahoma City truck bomb, and additional traffic restrictions were imposed around the White House after Sept. 11.

Washington, D.C. Mayor Anthony Williams said he would work with federal officials to implement the ban, but expressed hope the federal government would help the city relieve traffic problems arising from the security measures.

Williams also said the administration had agreed to study the possibility of building a tunnel near the White House area to help alleviate traffic. Other construction projects or shuttle systems were also possibilities, he said.

"While we are committed to working closely with federal officials on security issues, we cannot permit the loss of additional on-street parking spaces or the closure of additional sections of road on a piecemeal basis," Williams said in a statement. Nampa-Reuters