Lebanese security forces have raided the Beirut home of a man they identified as a Palestinian who appeared in a video claiming responsibility for the killing of a former Lebanese prime minister.
A Lebanese security source said Ahmed Aboul Adef was not in the house.
He had earlier appeared in a video aired by Al Jazeera claiming responsibility for the killing of former Lebanese prime minister Rafiq al-Hariri.
Meanwhile, the assassination of the former leader has attracted outrage.
Lebanese opposition figures are claiming Syria and Lebanese authorities are responsible for the car bombing and have called for the government's resignation.
In a statement read to reporters after an emergency meeting in Beirut, opposition figures also called for Syrian forces to pull out before elections in May, as well as a three-day strike.
"The opposition holds the authorities in Lebanon and Syria, the guardian power, responsible for this crime ... and calls on the international community to shoulder its responsibilities towards Lebanon , the captive nation," they said. It did not clarify the nature of responsibility.
"(The opposition) demands the departure of the authority that has lost its constitutional, popular and international legitimacy and calls for a neutral transitional government and the pull-out of Syrian forces before the elections."
Druze chief Walid Jumblatt and Christian ex-president Amin Gemayel were among the most prominent figures at the meeting.