Hezbollah Secretary-General Hassan Nasrallah made the call in a speech broadcast live on the al-Manar network, saying the Western-backed government was a failure, Lebanon's Daily Star reported.
"The government's failure is the result of its being a one-camp government. In Lebanon, in its ethnic and multi-colored composition, one camp cannot rule," Nasrallah said. "This government has proved that it is unable to meet its obligations and it has failed, and therefore we call for a unity government."
Nasrallah said the protest will represent all opposition parties, and not just Hezbollah, YNetNews reported.
"Our aspiration is to establish a unity government which will be based on solidarity and understanding, and not on imposing one party's positions on the other," he said.
The move was not a surprise to Siniora, as security forces have been deploying troops and armored vehicles outside government offices for the past two days.
Wisconsin business offering 'therapeutic cuddling' forced to close
Workers accuse National Zoo of animal mismanagement