Tensions are mounting over a UN-backed tribunal investigating the 2005 assassination of former Prime Minister Rafik Hariri. Many fear that Hezbollah — widely expected to be named in the indictments —will react violently if accused.

A senior security official confirmed to The Associated Press that the security measures in and around Beirut stem from “concerns of movements on the ground by some parties.”

Special police forces were seen hauling cement barriers around the government house in Beirut and putting up reinforcements around government buildings and banks. Armored personnel carriers deployed in many areas of the city.

The new measures follow the departure from Beirut of Qatari and Turkish mediators after two days of talks that failed to resolve the differences between Lebanon's main rival factions and bring them back together in a coalition government.

Qatar and Turkey suspended their mediation Thursday, saying it was time for Lebanese themselves to tackle the dispute. Turkish Foreign Minister Ahmet Davutoglu, speaking after two days of talks in Beirut with Lebanon's political leaders, said he and Qatari Prime Minister Sheikh Hamad bin Jassim Al-Thani had failed to win agreement for their proposals.

He spoke a day after Saudi Arabia said it was abandoning mediation efforts with rival Syria, deepening uncertainty in the country.

"We presented a draft to all sides that included their demands and was based on the Syrian-Saudi Arabian initiative," Davutoglu said, referring to earlier efforts by Damascus and Riyadh to contain tensions in Lebanon over the indictment.

"The final decision lies with Lebanese groups ... This morning we saw from the reactions and responses made to us that there were still some reservations," he told reporters in Istanbul after leaving Beirut shortly before dawn. "However, if they take a new approach, we are always ready to show effort for Lebanon's stability. But rather than a new effort from us, it's time for the sides to think."

The political confrontation in Lebanon, which suffered 15 years of civil war from 1975-1990, revived fears of more recent violence in May 2008, when gunmen took over parts of Beirut in response to government moves against Hezbollah.