NEW YORK, March 28 - Police closed New York's Williamsburg Bridge on Friday after three men were arrested for climbing on it, but said the incident was not terrorism-related. A police spokesman said the bridge, one of several linking Manhattan to the borough of Brooklyn on the East River, was being searched by police and other emergency units who have been on high security alert since the U.S. led war on Iraq started last Thursday. "We do not believe it is terrorist related," said an official with the New York Police Department, which has been on highest alert since the Sept. 11, 2001, attacks. "There is no suspicious package." Police source said they believed the incident may have been a prank by the three men.//