One man was killed and two were injured after clashes erupted in the northern Lebanese city of Tripoli, according to security sources.

Gunmen engaged in street skirmishes in the Alawite Jabal Mohsen area and the Bab Al Tabbaneh district that is mainly inhabited by Sunnis.

Lebanese troops on Monday launched a major security operation to quell the fighting that was touched off by the assassination of a top anti-Syrian intelligence chief.

The assassination on Friday, blamed by many on the Syrian regime, has stirred up sectarian violence in Lebanon where people are deeply divided between supporters and opponents of President Bashar Assad's government in Damascus.

Syria has intervened heavily in Lebanese affairs over the past decades and is blamed for the deaths of many prominent critics and anti-Syrian political figures.

Intelligence chief Brigadier General Wissam al-Hassan was a Sunni who challenged Syria and its powerful Lebanese ally, the Shiite militant group Hezbollah.

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.

In the capital Beirut on Tuesday, the army had restored calm to the streets as the European Union Foreign Policy chief Catherine Ashton arrived for meetings with the Lebanese leadership.

Ashton condemned the violence of the past few days and offered the EU's support "for the unity of the country".

"I welcome the efforts undertaken to maintain stability through national dialogue and I encourage all political leaders to work towards constructive solutions to the main challenges that face Lebanon today," she said.

She also thanked Lebanon and other neighbours of Syria for providing support to those Syrians forced to flee violence in their country.

Ashton held talks with Lebanon's Prime Minister Najib Mikati, President Michel Suleiman and parliament speaker Nabih Berri.

The foreign policy chief is in the region for talks on recent developments, particularly the 19-month-old conflict in Syria and its repercussions for instability in neighbouring countries.