The United States on Thursday expressed outrage over what it called Zimbabwe's unjust detention of U.S. diplomats and said it would raise the issue at the United Nations.

State Department spokesman Sean McCormack said the diplomats, who were stopped at a roadblock north of Harare, the capital, had been released. The U.S. ambassador in Zimbabwe said police slashed tires and grabbed phones, and that "war veterans" threatened to burn the vehicles with the officials inside.

"While this immediate incident has been resolved, it will not be forgotten," McCormack warned.

"It is absolutely outrageous, and it is a case of the kind of repression and violence that this government is willing to use against its own people," he told reporters at the State Department.

McCormack said the U.S. plans to raise the matter at the U.N. Security Council to register "deep concern, unhappiness, and distress" and to "highlight the fact that the international system is watching events in Zimbabwe and that the actions by the Mugabe government will not go unremarked."

"It signals our intention that we are going to continue to press this matter," he said.

McCormack said the U.S. also planned to complain directly to Zimbabwean diplomats attending a U.N. food conference in Rome and to the government in Harare.

Opposition and rights groups have accused President Robert Mugabe of orchestrating violence and intimidation in the run-up to a June 27 presidential runoff.

Zimbabwean police spokesman Wayne Bvudzijena denied security agents had threatened the diplomats, saying instead that police were trying to rescue them from a threatening mob.

McCormack dismissed as absurd any suggestion that the Zimbabwean government did not know of the U.S. officials' plans to travel outside Harare.

U.S. Ambassador James McGee, who was not with the convoy, told CNN that Zimbabwean police, military officers and so-called war veterans, a group of fiercely loyal and often violent supporters of Mugabe, were responsible for what he called an "illegal action."

"Zimbabwe has become a lawless country," McGee said, adding that he believes the orders of intimidation are "coming directly from the top."