The United States and the European Union have expressed concern at the political situation in Lebanon, where the opposition has called for the premier to step down over a deadly blast blamed on Syria.
EU foreign policy chief Catherine Ashton on Tuesday cautioned against a political vacuum in Lebanon at the end of a visit to the country, echoing comments from the State Department.
Ashton also warned that "there are some who are trying to divert attention from the situation in the region by causing problems in Lebanon," without saying who, Lebanon's National News Agency (NNA) reported.
Her concerns were highlighted when an opposition MP said he and four colleagues had received texted death threats from a Syrian telephone number before and after Friday's car bombing in Beirut.
The blast killed police intelligence chief General Wissam al-Hassan, who had led a series of investigations linking the regime of President Bashar al-Assad to political assassinations in Lebanon.
"This attack is a terrible thing; we are concerned about the stability of Lebanon," Ashton was quoted as saying after meeting Prime Minister Najib Mikati.
US State Department spokeswoman Victoria Nuland said Washington backed efforts by President Michel Sleiman and other leaders to build an effective government.
"President Sleiman is engaged in discussions with all parties to form a new government," she said. "We support that process.
"In the interim, we don't want to see a vacuum," she added.
Ammar Houry, an MP with the fiercely anti-Assad opposition movement of Saad Hariri, said on Monday that "on the eve of the attack, we received an SMS from a Syrian number that read: 'Sons of bitches, we will get you one by one'."
They did not pay much attention to it until Hassan was killed, he added.
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Afterwards, "we received a second SMS that read: 'Congratulations, the countdown has begun. One of 10 eliminated.'"
Hassan's murder has sparked fears of new sectarian strife in Lebanon, where much of the Sunni Muslim community opposes Assad's regime and most Shiites support him, while Christians are divided.
Since Friday's bombing, at least 11 people have been killed in fighting between pro- and anti-Syrian camps in the northern city of Tripoli, including a woman who died on Tuesday.
The city is a bastion of anti-Assad sentiment but also home to a minority of Alawites, who belong to the same offshoot of Shiite Islam as Assad.
There has also been scattered violence in Beirut since the bombing, with a Palestinian youth killed, but the capital was calm on Tuesday.
Hariri and other opposition figures have blamed Damascus for the assassination of Hassan and demanded the resignation of Mikati, whose cabinet is dominated by the Syrian-backed Hezbollah.
Mikati expressed a desire to step down but said on Saturday he would stay at the request of Sleiman in the "national interest".
In a separate meeting with Sleiman, Ashton expressed her concerns of a possible political vacuum and the EU's commitment to the "sovereignty, independence and stability of Lebanon," the NNA said.
Ashton also met parliament speaker Nabih Berri and former premier Fuad Siniora, who heads Hariri's parliamentary bloc, before flying out at the end of a visit that had been planned before the Beirut bomb blast.
On Monday, the ambassadors of Britain, China, France, Russia and the United States expressed their "unequivocal condemnation of any attempt to destabilise Lebanon through political assassination".
Hariri, himself a former premier, has said he was determined to oust Mikati's government "by peaceful and democratic means." However, analysts have said that unless Mikati willingly resigns, the government will stay in place.
Lebanon is also being affected by a flood of refugees from Syria, with the UN refugee agency saying on Tuesday that the number had topped 100,000.