BEIRUT (AP) — Calm returned to the streets of Lebanon’s capital on Tuesday, a day after troops launched a major security operation to quell fighting touched off by the assassination of a top anti-Syrian intelligence chief.

The country’s police chief late Monday released details of the investigation into the killing of Brig. Gen. Wissam al-Hassan, describing a carefully planned car bombing that targeted the intelligence officer as he was moving about the capital in secret.

Many in Lebanon blame Syria for the killing. Damascus has intervened heavily in Lebanese affairs and is blamed for the deaths of many prominent critics. Al-Hassan was a Sunni who challenged Syria and its powerful Lebanese ally, the Shiite militant group Hezbollah.

Seven people have died in clashes between pro- and anti-Syria factions sparked by the Friday assassination. The blast, the deadliest in Beirut in four years, killed two people in addition to al-Hassan.

Maj. Gen. Ashraf Rifi told a group of journalists that al-Hassan was assassinated outside one of his secret offices where he used to meet with informants. He was driving an unarmored rented car for camouflage. Al-Hassan was one of Lebanon’s most secretive figures, and until his death many Lebanese did not know what he looked like.

“The martyr Wissam had an appointment in this office and it seems he was watched,” Rifi said, adding that the booby-trapped car went off as al-Hassan’s car was passing slowly by through the narrow street. The secret office in the predominantly Christian neighborhood of Achrafieh is few hundred meters (yards) away from the heavily-fortified police headquarters where al-Hassan spent most of his time while in Lebanon.

He also said investigators had identified the car used in the bombing as one stolen a year earlier.

Rifi confirmed reports from Washington that an FBI team will arrive to help in the investigation in the next two days. FBI teams helped investigate several bombings since 2005.

A senior security official, speaking on condition of anonymity in line with regulations, said al-Hassan entered through Beirut’s airport using a fake name and after he reached his office, he sent his passport to the airport to be stamped. The official said this could be one of the ways how it became known al-Hassan is in Lebanon.

The official added that al-Hassan was supposed to stay in Paris with his family for more than week to celebrate the Muslim feast of Eid al-Adha that starts Friday, but it is not clear why he returned to Lebanon.

The circumstances were similar to two other assassinations of Damascus critics: the 2005 killing of newspaper editor and lawmaker Gibran Tueni and the 2007 death of Christian lawmaker Antoine Ghanem from the right-wing Phalange Party. Both died in car bomb blasts shortly after returning to Lebanon from abroad, in secret.

The daily As-Safir reported that security authorities now have the data of al-Hassan’s mobile phone and are checking it specifically from the time he landed in Beirut until he was killed. His last call was to former Prime Minister Saad Hariri, telling him he was in Beirut.

Al-Hassan was very close to Hariri and in the past was in charge of the security of his father, former Prime Minister Rafik Hariri. He investigated Hariri’s killing by a truck bomb in 2005, also widely blamed on Syria. An international tribunal indicted four members of Hezbollah for Hariri’s killing, although the group denies involvement.

Al-Hassan’s work led to the arrest of former Information Minister Michel Samaha, one of Syria’s most loyal allies in Lebanon, who is accused of plotting a wave of attacks in Lebanon at Syria’s behest. Syrian Brig. Gen. Ali Mamlouk, one of Assad’s most senior aides, was indicted in absentia in the August sweep.

Officials say his department also had a role in breaking up several Israeli spy rings inside Lebanon in recent years. Israel has never commented on the allegations.

The assassination has dramatically escalated political tensions and sparked violence between supporters of Syrian President Bashar Assad and his opponents. Lebanon and Syria share similar sectarian divides that have fed tensions in both countries. Most of Lebanon’s Sunnis have backed Syria’s mainly Sunni rebels, while Lebanese Shiites tend to back Assad, who belongs to the minority Alawite sect — an offshoot of Shiite Islam.

Angry protesters tried to storm the government palace after al-Hassan’s funeral on Sunday, venting their rage at leaders they consider puppets of the Syrian regime. But they were pushed back by troops who fired their guns in the air and filled the street with tear gas.

On Tuesday Prime Minister Najib Mikati, whose Cabinet is dominated by Hezbollah and its allies, resumed work at the palace and received EU foreign policy chief Catherine Ashton, who later met President Michel Suleiman.

Life in Beirut was normal Tuesday a day after troops conducted major operations opening roads and forcing gunmen out of the streets. Schools and businesses opened as usual.

In the northern city of Tripoli, security officials reported that the army deployed to separate gunmen from rival factions following sporadic exchanges of gunfire lasting until Tuesday morning.

Copyright 2012 The Associated Press.