Lebanese minister Adnan Sayyed Hussein resigned on Wednesday, the state news agency said, bringing to 11 the number of ministerial resignations and effectively collapsing the government of Prime Minister Saad al-Hariri.
Hussein's move followed the resignation of 10 ministers from Lebanon's Hezbollah movement and its political allies, who called on President Michel Suleiman to form a new government.
The resignation coincided with Prime Minister Hariri's meeting with US President Barack Obama in Washington.
Lebanon could now face a prolonged political impasse and heightened sectarian tension, but analysts said they did not expect any open military confrontation pitting Hezbollah, backed by Syria and Iran, against the Sunni Muslim followers of Hariri, who is supported by Saudi Arabia and the United States.
However, street protests, skirmishes or even a return to the bombings and political killings that followed Rafik al-Hariri's assassination in 2005 cannot be ruled out, the analysts said.
Lebanese politicians on Tuesday said
Saudi Arabia and Syria
had failed to forge a deal to curb political tensions in Lebanon over a UN-backed tribunal set up to try the killers of Hariri's father, former premier Rafik Hariri.
Disagreements over the investigation had paralyzed the "unity" government and revived fears of sectarian conflict.
Hezbollah has denied any involvement in the 2005 bombing which killed Rafik Hariri and 22 others. It has denounced the tribunal as an "Israeli project" and urged Saad Hariri to reject its findings - a demand he has resisted.
Hariri was due to meet US President Barack Obama in Washington shortly before the planned resignation announcement.