Pakistan's army Thursday threatened to review cooperation with the United States if it stages another similar violation of Pakistani sovereignty.

U.S. President Barack Obama lays a wreath at Ground Zero in memory of the 9/11 victims, four days after U.S. forces killed al-Qaida leader Osama bin Laden, in New York, May 5, 2011. The visit marked the first time Obama visited Ground Zero as president. [Wu Jingdan/Xinhua]

The army also called for cuts in the number of US military personnel in Pakistan in protest at the unilateral raid that killed the al-Qaida leader Osama bin Laden on May 1.

Pakistani army chief General Ashfaq Kayani told his colleagues that a decision had been made to reduce the number of US military personnel to the "minimum essential" levels.

The first statement of Pakistan since the US raid signaled the army's anger at the unilateral operation, but was also aimed at pacifying domestic critics who had accused it of failing to protect the country's sovereignty, potent charges in a country where anti-Americanism runs deep, a Shanghai Daily report said via agencies.

US President Barack Obama laid a wreath at Ground Zero Thursday to memorize the 9/11 victims. The visit marked the first time Obama visited Ground Zero as president.

Obama did not make any public comments during the wreath laying ceremony. The White House Press Secretary Jay Carney said "he wants to lay a wreath to honor the victims, to honor the first responders who so courageously rushed to the scene and in many cases gave their own lives to try to save others, to honor the spirit of unity in America that we all felt in the wake of that terrible attack. I think the power of that requires no words."

Before the ceremony, Obama met with the firefighters of Engine 54, known as the "Pride of Midtown", which lost 15 men on Sept. 11, 2001.

Obama announced on May 1 that bin Laden was killed by US forces at a compound in the Pakistani town of Abbottabad, which is located close to the capital, Islamabad.