In a televised address from Jidda, Saudi Arabia, on Saturday, Mr. Hariri's son, Saad Hariri, made a forceful call for a tribunal to oversee the issue, asking the international community "to support the international commission into the assassination of Mr. Hariri to bring out the full truth and bring the perpetrators to justice in an international court."
On Sunday, the country's Druse leader, Walid Jumblatt, flanked by members of his parliamentary block, echoed the call for an international court. "If necessary, we will support an international tribunal," Mr. Jumblatt told reporters from his home in the mountains about 20 miles from Beirut, while insisting that the report was based on "suspicions," not accusations against Syria.
The statements were both leaders' first public comments since Thursday, when the United Nations released a report on the investigation, led by Detlev Mehlis, that said the killing on Feb. 14 was a carefully planned terrorist act organized by high-ranking Syrian and Lebanese intelligence officers.
Mr. Jumblatt urged President Bashar al-Assad of Syria to cooperate fully with the investigation.
The calls came as Secretary of State Condoleezza Rice and the British foreign secretary, Jack Straw, said they were confident that there would be agreement at the United Nations Security Council for some form of action against Syria after the Mehlis report, although they did not specify what the action would be.
"I'm actually confident that we are going to get a response from the international system," Ms. Rice said, adding that it was "extremely important" that countries act together.
Ms. Rice said she had been on the telephone over the weekend, which she had spent traveling with Mr. Straw in her native state of Alabama, to decide more precisely what to do when the Security Council convenes, probably later in the week.
Mr. Straw also said that "there has to be a consensus" because the need for action was clear.
A special ministerial level session of the Security Council, planned for Tuesday, was expected to discuss imposing sanctions on Syria.
"The mere fact of having a Security Council meeting at ministerial level will send out a very sharp message indeed to the Syrians," Mr. Straw said in a BBC interview on Sunday.
Early Saturday, Lebanon arrested the first suspect identified in the United Nations report. The suspect, Mahmoud Abdel-Al, a member of the Ahbash Sunni Muslim Orthodox group with close ties to Syria, was detained on a warrant issued by Prosecutor General Saeed Meerza, an official said, speaking on condition of anonymity because he was not authorized to speak to the press about the matter. The police also seized documents from Mr. Abdel-Al's home.
The United Nations report said that a mobile telephone listed in Mr. Abdel-Al's name had dialed Lebanon's president, Émile Lahoud, minutes before the bombing that killed Mr. Hariri and 20 others. A spokesman for Mr. Lahoud denied that the president had ever been in contact with Mr. Abdel-Al.
The report also names Mr. Abdel-Al's brother, Ahmad Abdel-Al, as a major suspect in the plot, saying he had extensive contacts with Lebanese security officials before and after the attack.
On Sunday, Lebanon also placed a travel ban on 11 senior political and security officials who were suspected of involvement in the attack.