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.