Lebanon’s government was plunged into crisis yesterday after five cabinet members resigned in what appeared to be an attempt by Hezbollah, the Shiite militant group, to cause its collapse.

Prime Minister Siniora attempted to hold his government together by refusing to accept the resignations.

But Hezbollah piled on pressure by announcing street demonstrations this week to force the government to accede to the group’s demands for greater cabinet representation.

Hezbollah’s deputy leader, Sheikh Naim Kassem, said the resignations were the first step in a campaign that would be “varied and effective.”

Fears of bloody confrontations were raised as members of the ruling coalition promised counter-demonstrations.

All-party talks aimed at averting the crisis collapsed in Beirut on Saturday after Mr. Siniora’s allies rejected demands by Hezbollah and its allies for representation that would have given them sufficient power to veto key legislation.

The talks had been aimed at easing mounting sectarian tensions in the aftermath of the 34-day war between Hezbollah and Israel.

Hours after the talks broke down, the five cabinet ministers representing Hezbollah and its Shiite ally, the Amal movement, resigned. They included the foreign minister, Fawzi Salloukh, as well as the ministers for agriculture, health, energy, and labor. Under the Lebanese constitution, if eight ministers resigned, the government would have to be dissolved.

The Lebanese president, Emile Lahoud, said the resignation of all the ministers from the country’s largest religious faction meant any decisions made by the cabinet were invalid.

However, as things stand, he does not have the power to dissolve the government.

Mr. Siniora’s supporters claimed that pro-Syrian groups wanted the talks to fail to thwart the creation of an international tribunal into the assassination of the former prime minister, Rafik Hariri, last year.