Thousands of Hezbollah-led opposition protesters remain camped out near the offices of Siniora on the sixth day of demonstrations aimed at bringing down the government.
In a new tactic on Tuesday night, they aimed two powerful floodlights at the government complex. Troops installed more barbed wire and other fortifications.
Lebanon's political confrontation breaks down along dangerous sectarian lines. The US-backed government is supported largely by Sunnis, while the opposition, led by the pro-Syrian Hezbollah, enjoys wide support among Shias.
Lebanon's Christians are split between the two camps.
Hezbollah is demanding the formation of a new government giving it and its allies a larger share of power.
The calls to ease the sectarian tension came amid warnings from the army commander that the trouble could get out of control despite the deployment of thousands of soldiers who have been rushing reinforcements from one district to another across the capital in an attempt to keep order.
"The absence of political solutions, along with the recurring security incidents, particularly those with sectarian tinge, drains the army's resources and weakens its neutrality," Suleiman was quoted by several Beirut papers as saying.
"This weakness will make the army unable to control the situation in all areas of Lebanon," he said after touring the unrest areas on Monday and then meeting with the prime minister.
The death of a Shia anti-government
protester has inflamed sentiments
Suleiman's reported remarks were exceptional in that army officers are not allowed to make political statements.
Soldiers and armoured cars have taken up positions in various parts of Beirut, particularly around Siniora's office complex. Soldiers are also on duty in the Sunni and mixed neighbourhoods where nightly riots with sticks, bottles and sometimes gunfire have occurred.
The standoff shows no sign of waning despite calls from both sides for dialogue to resolve their differences. The Arab League secretary-general has visited to try to help, as has Jordan's foreign minister. Egypt's Beirut envoy is also making the rounds.
After several days of trading accusations in the media, rival Lebanese leaders opened direct channels.
A Sunni scholar in the opposition went to the government headquarters to discuss ideas on resolving the crisis and the government gave him its own proposals, including the possible expansion of the current cabinet to satisfy opposition demands, Ahmed Fatfat, a Lebanese interior minister, said.
Shia leaders have tried to prevent revenge attacks after the killing of a Shia protester, who was shot on Sunday while walking with other protesters through a Sunni neighbourhood.
In a district close to the shooting scene, Shia Amal party members and relatives of the slain man took turns carrying his coffin.
About 2,000 people, many holding Lebanese and green Amal flags, marched behind. A scout band played martial music. Some of the Shias beat their heads with their hands in a traditional sign of mourning.
The funeral march made its way through a street to the Rawdat al-Shahidein cemetery, where Abdul-Amir Kabalan, a senior Shia cleric, led the prayer over the coffin amid the wails of relatives and calls of "Allahu Akbar," or God is great.
Street clashes from Shia-Sunni tensions have also left 23 people injured.
"It is (religiously) prohibited for a Shia to kill a Sunni, a Sunni to kill a Shia, a Druse to kill a Shia, a Shia to kill a Druse and a Christian to kill a Muslim," said Kabalan, the deputy leader of the Supreme Shiite Council, the religious governing body of the 1.2 million Shia, Lebanon's largest sect.
"It is prohibited to fight each other, to provoke and curse each other."
Ayoub Hemayed, a senior member of Amal, a major Hezbollah ally, urged supporters to exercise restraint. "We will not be dragged into sedition ... We are called upon to remain one hand and united."