President George Bush says America's greatest challenge is stopping terrorist leader Osama bin Laden from attacking the country again. The president spoke at the swearing-in of the new Director of Homeland Security.

President Bush says U.S. forces are on a constant hunt for bin Laden, whose al-Qaida terrorist group was behind the September 11, 2001 attacks in New York and Washington.

The president referred to recent intelligence reports that bin Laden is trying to recruit Jordanian-born terrorist Abu Musab al-Zarqawi to organize attacks outside Iraq.

President Bush says coalition and Iraqi forces are working day and night to dismantle al-Zarqawi's terrorist network in Iraq and bring him to justice. At the same time, Mr. Bush says U.S. troops are keeping the pressure on bin Laden, keeping him in hiding.

"Bin Laden's message is a telling reminder that al-Qaida still hopes to attack us on our own soil. Stopping him is the greatest challenge of our day," the president said.

The president spoke following the swearing-in of former judge and federal prosecutor Michael Chertoff as America's new Director of Homeland Security.

"Mike Chertoff knows we can not afford to become complacent. He understands that as we adapt our defenses, the terrorists will adapt their tactics in response. He understands they continue to pose a grave threat to the American people," Mr. Bush said.

The president says U.S. actions since the September 11 attacks have already made the world safer by toppling regimes in Iraq and Afghanistan, convincing Libya to give up its weapons of mass destruction, and breaking-up the nuclear trading network of Pakistani scientist A.Q. Khan.

Mr. Bush says while confronting terrorists abroad makes Americans safer at home, there can be no let up in protecting U.S. borders.

"We have been relentless and we will continue to be relentless in our mission to secure the people of this country," the president said. "From Florida to California to Massachusetts, we have arrested and prosecuted terrorist operatives and their supporters. By our actions we are sending the world a clear message: 'The terrorists will not be permitted sanctuary or safe haven or the tools of mass murder'."

Secretary Chertoff takes charge of an agency with 160,000 employees from border patrol and Secret Service to the Coast Guard and immigration control. He succeeds former Pennsylvania Governor Tom Ridge who was the nation's first Director of Homeland Security, following the biggest government reorganization since World War II.