Updated

President Bush celebrated a major success in the fight against terrorism Saturday with the arrest of the Al Qaeda operative suspected of planning the Sept. 11 attacks.

"That's fantastic!" the president said early Saturday when his national security adviser, Condoleezza Rice, delivered the news of Khalid Shaikh Mohammed's capture in Pakistan.

CIA officers and Pakistani authorities carried out the operation that led to Mohammed's capture, according to American officials, who spoke on the condition of anonymity.

It was unclear whether Mohammed had been taken into U.S. custody or where he was being held.

It was midnight Friday when CIA Director George Tenet first called Rice, who was staying at Camp David with the president and first lady, to say that authorities were "pretty certain" they had Mohammed and two others, White House press secretary Ari Fleischer.

The confirmation came first thing Saturday and Rice called from her cabin to Bush's at the Maryland mountain retreat.

"It's hard to overstate how significant this is," Fleischer said. "It's a wonderful blow to inflict on Al Qaeda."

Fleischer described Mohammed as a "savvy operational planner" of the terrorist network and a nuts-and-bolts leader.

A White House statement accused Mohammed of masterminding the attacks on Washington and New York and of being "centrally involved" in Al Qaeda plotting since then for attacks inside the United States.

"This is a great success today, but the war on terrorism goes on tomorrow," said U.S. Central Command spokesman Jim Wilkinson. "There's still a lot of work to do."

Former New York Mayor Rudy Giuliani said the arrest was "a significant indication that our government is pursuing an effective and consistent international policy to reduce the threat of global terrorism."

It is too soon for decisions about whether Mohammed might be the first defendant Bush designates for trial before a military tribunal or dealt with some other way, Fleischer said. Officials would not comment on whether Mohammed was to be brought to the United States.