Some 100 MPs of the 128-member house were taking part in the protest at the parliament building in central Beirut that opened on Saturday with a minute's silence in memory of the 1,200 Lebanese, almost all civilians, killed in the offensive.
Nabih Berri, the parliament speaker, in a speech urged fellow Arab countries to defy the air and sea blockade by sending boats to Lebanon without seeking authorisation from the Israelis.
The international community, Berri said, should "take all necessary measures to lift the Israeli blockade which constitutes an extension of Israel's terrorist war".
Aljazeera quoted Berri as saying that Arab delegations should visit the ambassadors of the five permanent member states of the UN Security Council, as well as the ambassadors of the Arab countries which enjoy relations with Israel, to urge them to freeze relations as long as the siege on Lebanon remained.
The blockade, in force since the war erupted after Hezbollah captured two Israeli soldiers on July 12, was "not only being imposed on Lebanon but also the United Nations and (Security Council) Resolution 1701", he said.
The resolution brought a halt to 34 days of deadly clashes between Israel and the Hezbollah and called for the blockade to be lifted.
Berri, who called the sit-in during a visit on Thursday to south Lebanon, which bore the brunt of the fighting, told the mass-circulation daily An-Nahar that it would continue "night and day until the lifting of the blockade".
Before the closure is lifted, Israel insists on a significant deployment of foreign forces, as also called for by Resolution 1701, to curb arms deliveries to Hezbollah which has defied Security Council calls for its disarmament.