U.S. Secretary of State Condoleezza Rice Wednesday accused Syria of obstructing the U.N. inquiry into last year's assassination of former Lebanese Prime Minister Rafiq Hariri. She threatened to send the matter back to the U.N. Security Council if Syrian interference continues.

The U.S. warning came in a strongly worded written statement by the secretary of state, who said Syria must cease obstructing the Hariri probe, and that the United States intends to refer the matter back to the Security Council if the obstruction continues.

The statement comes at a critical juncture, with a new prosecutor - Belgian jurist Serge Brammertz - taking over the U.N. probe, and investigators seeking to interview Syrian President Bashar Assad about the Hariri killing.

Investigators have already said in reports to the Security Council that they believe Syrian intelligence officials and Lebanese allies were probably behind the car bomb attack last February that killed Mr. Hariri and 22 others.

Attention on President Assad has intensified since a statement two weeks ago in Paris by former Syrian Vice President Abdel-Halim Khaddam, who said the Syrian leader had threatened Mr. Hariri in harsh and explicit terms only months before the killing.

In her statement, Secretary Rice said Syria must once and for all end its interference in Lebanese internal affairs under terms of U.N. Security Council resolution 1559 of September 2004.

She said continuing assassinations of Lebanese opponents of Syrian domination, including last month's killing of journalist and legislator Gebran Tueni create an atmosphere Syria uses to intimidate Lebanon.

She said the intimidation must end and that Syria must immediately come into compliance with all relevant U.N. resolutions.

At a subsequent news briefing, State Department Spokesman Sean McCormack said the United States, at this point, is not drawing a direct link between Syria and the assassinations.

"But I think it's very clear that there are forces in Lebanon that may be sympathetic to Syria and the Syrians' position and whose interests are linked to Syria that are trying to foment an atmosphere of instability, an atmosphere of fear, through the use of threats, violence and assassinations. That has to end," he said.

The Rice statement said the United States stands firmly with the people of Lebanon in rejecting any deal or compromise that would undermine the U.N. investigation, or relieve Syria of its obligations under Security Council resolutions.

She also said the United States calls for full implementation of all parts of resolution 1559, including the disarmament of Hezbollah and other militias.

She said Syria's continued provision of arms to Hezbollah and Palestinian terrorist groups destabilizes Lebanon and make terrorist attacks possible within Lebanon and from Lebanese territory.

The pro-Iranian Hezbollah has essentially controlled a strip of territory along Lebanon's border with Israel since Israeli forces withdrew from their self-described Lebanese security zone in 2000.

Resolution 1559 calls for the extension of the control of the government of Lebanon over all Lebanese territory.