"The gathering affirms ... that the president is providing protection for the existing political security system and is responsible for its acts," it said in a statement on Thursday issued after meeting to discuss the killing of an anti-Syrian politician this week.
"The president's departure would be a main path to law and justice," the group said.
The Lebanese opposition has vowed to bring an end to the assassinations by swooping in on what they say is a security system controlled by President Emil Lahoud, Aljazeera's correspondent in Lebanon Abbas Nasir said.
Despite the opposition's victory led by Saad al-Hariri, political violence continues. The opposition looks at recent bombings as an attempt to foil its political victory, he said.
Some opposition groups have described local Lebanese parties as "Syria's mercenaries", accusing them of supporting the explosions in collusion with the security forces.
The aim, as they see it, is to ensure that Lebanon has no say in its internal affairs.
"Throwing readymade and hasty accusations will only set the stage for international powers to meddle in Lebanese affairs," head of the Syrian National Party, Jabran Ariji said.
The Lebanese opposition says
security is controlled by Lahoud
"When Rafiq al-Hariri was assassinated, we urged Karami to resign.
"But nowadays we do not see anyone firing questions at the interior minister," said Ibrahim Kanan, a member of parliament linked to Michel Aoun, who allied with pro-Syrian parties in the elections.
The coalition called for a general strike on Friday in protest against the killing of George Hawi, a former head of the Lebanese Communist Party and a critic of Syria, and urged Lebanese to turn out in force for his funeral, also on Friday.
Hawi was killed when a bomb exploded in his car on Tuesday. On 2 June, newspaper columnist Samir Kassir was killed in a similar explosion.
The killings have followed the assassination of former prime minister al-Hariri on 14 February and the withdrawal of Syrian troops from Lebanon in April.
Lahoud has denounced the killings and says he will stay on until the end of his term in a little over two years.