EU foreign policy chief Catherine Ashton warned on Tuesday against a political vacuum in Lebanon after the opposition called for the premier to step down over a deadly blast blamed on Syria, state media said.
She also claimed, without pointing a finger, that "there are some who are trying to divert attention from the situation in the region by causing problems in Lebanon," the National News Agency 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.
The blast in Beirut killed police intelligence chief General Wissam al-Hassan, who 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.
Ammar Houry, an MP with the fiercely anti-Assad opposition movement of Saad Hariri, said Monday night 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'."
He said they did not pay much attention to it until Hassan was killed.
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 inter-confessional strife in Lebanon, where much of the Sunni Muslim community opposes the regime of Syrian President Bashar al-Assad and most Shiites support him. Christians are divided on the subject.
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Since the bombing, at least 12 people have been killed and wounded in fighting in the northern city of Tripoli, including a woman who died on Tuesday.
The city is a bastion of anti-Assad sentiment but also includdes a minority of Alawites, who belong to the same offshoot of Shiite Islam that Assad does.
There has also been scattered violence in Beirut since Friday's bombing, in which a Palestinian youth was killed.
Anti-Syria opposition chief Saad Hariri and other political figures have blamed Damascus for the assassination and demanded the resignation of Mikati, whose cabinet is dominated by Syrian ally Hezbollah.
Mikati, who expressed his desire to step down, said on Saturday he would stay at the request of President Michel Sleiman in the "national interest."
In a separate meeting with Sleiman on Tuesday, Ashton expressed her concerns of a possible political vacuum and the EU's commitment to the "sovereignty, independence and stability of Lebanon," the National News Agency said.
On Monday, the ambassadors of Britain, China, France, Russia and the United States had expressed their "unequivocal condemnation of any attempt to destabilise Lebanon through political assassination".
Hariri, a former premier who heads the parliamentary opposition, 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 the number had risen to 100,000.
Ashton's visit to Lebanon, planned before the attack, is the second leg of a five-day regional tour ending in Jerusalem.
She was to hold a press conference at Beirut's international airport later Tuesday.