"I promise this to the people of Darfur: the United States will not avert our eyes from a crisis that challenges the conscience of the world," the president said.
The sanctions target government-run companies involved in Sudan's oil industry and three individuals, including a rebel leader suspected of being involved in the violence in Darfur.
"For too long the people of Darfur have suffered at the hands of a government that is complicit in the bombing, murder and rape of innocent civilians," the president said. "My administration has called these actions by their rightful name: genocide.
"The world has a responsibility to put an end to it," Mr. Bush said.
The president had been prepared to impose the sanctions last month, but held off to give U.N. Secretary-General Ban Ki-moon more time to find a diplomatic end to the four-year crisis in Darfur where more than 200,000 people have been killed.
Ban said at the United Nations on Tuesday that he still needed more time to promote political negotiations and persuade the Sudanese government to accept more peacekeepers. Asked whether the U.S. sanctions would complicate his job of getting Sudan to agree to a larger U.N.-African Union peacekeeping force, Ban said: "We will have to see."
Sudan's government criticized Mr. Bush's action. "We believe this decision is unfair and untimely," Sudan's Foreign Ministry spokesman Ali Sadiq told The Associated Press. He urged the rest of the world to ignore the U.S. move.
Beyond the new U.S. sanctions, Mr. Bush directed Secretary of State Condoleezza Rice to draft a proposed U.N. resolution to strengthen international pressure on the Sudanese government of President Omar al-Bashir.
Save Darfur Coalition director David Rubenstein welcomed the sanctions, but said they might be too little, too late.
"President Bush must not give further months to determine whether these outlines measures work — the Darfuri people don't have that much time," he said. "The president must set a short and firm deadline for fundamental changes in Sudanese behavior, and prepare now to implement immediately further measures should Khartoum continue to stonewall."
Mr. Bush said he delayed imposing sanctions last month to allow more time for diplomacy, but that al-Bashir has continued to make empty promises of cooperation while obstructing international efforts to end the crisis.
"One day after I spoke, they bombed a meeting of rebel commanders designed to discuss a possible peace deal with the government," the president said. "In the following weeks he used his army and government-sponsored militias to attack rebels and civilians in south Darfur. He's taken no steps to disarm these militias in the year since the Darfur peace agreement was signed. Senior officials continue to oppose the deployment of the U.N. peacekeeping force.
"The result is that the dire security situation on the ground in Darfur has not changed," Mr. Bush said.
"The President's multi-track policy of imposing unilateral U.S. sanctions along with international sanctions while supporting U.N. and African Union peacekeeping forces with humanitarian, financial and military assistance, provides a moral high ground that has a better chance of stopping the brutal bloodshed in Darfur," comments CBS News foreign affairs analyst Pamela Falk.