WASHINGTON, Sept. 11 (Xinhuanet) -- The United States on Sunday marked the fourth anniversary of the Sept. 11 terror attacks by various memorial activities.

    In a customized ritual, US President George W. Bush and Vice President Dick Cheney and their wives led the observance of a moment of silence at 8:46 a.m. (1346 GMT), the exact minute in 2001 when terrorists smashed the first jetliner into the World Trade Center, New York.

    As local TV news footage showed, the two presidential couples, all in dark suits, held their hands over their hearts, facing south to the Washington Monument.

    US cabinet members, policy advisers and White House working staff also attended the ceremony.

    Earlier, the two presidential couples joined a prayer service for the victims and survivors of Sept. 11 attacks at St. John's Episcopal Church on Lafayette Park across from the White House.

    Meanwhile, a major memorial event was being held at Ground Zero, New York, to remember the 2,749 people who died four years ago.

    In his weekly radio address on Saturday, Bush linked this year's observance to Hurricane Katrina which devastated the US Gulf Coast on Aug. 29.

    As it holds the observance, he said, the United States is "confronting another disaster that has caused destruction and lossof life."

    "This time the devastation resulted not from the malice of evilmen, but from the fury of water and wind," Bush said.

    He promised that the nation "will overcome this ordeal, and we will be stronger for it."

    On Saturday, US Defense Department sponsored a "Freedom Walk" event in Washington to honor US troops in Iraq.

    The part of the Pentagon where a third jet crashed on Sept. 11 was opened up to the public for the first time.

    As the Bush administration tried to show its resolve on the "war against terror" and rally public support in this year's memorial activities, recent opinion polls showed that many Americans feel no safer from the threat of another terrorist attack.

    The Washington Post reported Sunday that four years after the terror attack, the nation's capital still lacks a comprehensive way to tackle a major emergency including a terror attack. Enditem