The State Department said Thursday the United States has raised concern with Libya "at the highest levels" about reports that country may have been involved in a plot to assassinate the de facto ruler of Saudi Arabia, Crown Prince Abdullah. It said Libya has responded with an assurance that it would not use violence to settle disputes with any state.

Officials here are declining comment on specifics of the plot allegations raised in a front-page story Thursday by the New York Times.

But they say the matter has been taken up directly with authorities in Tripoli, including Libyan leader Muammar Gadhafi, and that the United States has been told that Libya has no future intention of using violence to settle disputes with other countries.

The New York Times quoted U.S. officials as saying that two participants in the alleged plot, one detained in the United States and another in Saudi Arabia, have given detailed accounts of the conspiracy, under which Libyan intelligence was to have financed an attack on Crown Prince Abdullah in the Muslim holy city of Mecca.

At a news briefing, State Department spokesman Richard Boucher said reports came to the attention of the United States late last year that Libya had been in contact with Saudi dissidents who had threatened violence against the Saudi royal family.

Mr. Boucher said the United States raised the issue at several meetings with the Libyans, including a meeting in March between Mr. Gadhafi and assistant Secretary of State William Burns that was the highest-level contact between the two governments in more than a decade.

While side-stepping the issue of whether the United States believes the plot existed, Mr. Boucher said Libya pledged, at least from that point on, not to use violence to settle scores with other countries.

"I'm not going to get into questions of the truth of the allegations. I'm going to tell you that we went directly to the Libyans," he said. "The Libyans have told us that they would not support, they would not support, that they would not support the use of violence for settling political differences with any state, and that is a promise and a commitment that we expect to hold them to."

Libyan leader Gadhafi, who overthrew a monarchy when he took power in 1969, has long had a bitter rivalry with the Saudi royal family.

But spokesmen for the Libyan government, including Mr. Gadhafi's son, have categorically denied that country was involved in an assassination plot against the Saudi leadership.

Under questioning here, Mr. Boucher said the plot allegations have not prompted the Bush administration to reconsider recent steps toward normalizing relations with Libya, propelled by that country's decision last December to renounce weapons of mass destruction.

But he said the ongoing investigations of the alleged conspiracy by U.S. and Saudi authorities would affect the timetable for the lifting of remaining sanctions against Libya, linked to its continued presence on the State Department's list of state supporters of terrorism.

He said to remove Libya from the list, the Bush administration would have to be able certify to Congress that Libya has had no connections with terrorism or terrorist groups for a period of at least six months, something he made clear it cannot do under the present circumstances.