BEIRUT (Reuters) - Lebanese President Michel Aoun called for forgiveness and stability on Tuesday after a political row involving his son-in-law triggered street protests and deepened a rift with Parliament Speaker Nabih Berri.

Slideshow ( 2 images )

Berri supporters set tyres ablaze and blocked roads on Monday in protest against comments by Aoun’s son-in-law, Foreign Minister Gebran Bassil who had called him “a thug” in a video that circulated on social media.

“What happened on the ground is a big mistake based on a mistake,” Aoun said in a statement. “I forgive all those who assaulted me and my family, and I look to those who insulted each other to forgive each other,” he said.

The Free Patriotic Movement party, founded by Aoun, said Bassil had already expressed regret for the comments and it regarded the issue as over.

Berri supporters, who have been demanding a public apology from Bassil, protested again after the FPM statement, briefly setting fires in a main road in Beirut, security sources said.

Political tensions between Berri, a Shi’ite, and Aoun, a Maronite Christian, have been escalating since December when Aoun signed a decree promoting dozens of army officers without the signature of Shi’ite Finance Minister Ali Hassan Khalil, one of Berri’s closest aides.

The row threatens to ignite sectarian tensions in the run-up to a parliamentary election in May, and risks paralyzing Prime Minister Saad al-Hariri’s coalition government which groups nearly all of Lebanon’s main parties.

In one incident on Monday, gunfire erupted near the offices of Aoun’s Free Patriotic Movement (FPM) east of Beirut. The FPM and the Amal movement led by Berri traded blame.

Bassil expressed regret for his remarks in an interview with the Lebanese al-Akhbar newspaper on Monday, saying he had departed from his moral standards in the closed meeting.

But this did little to ease fury in the Berri camp, which has said Bassil crossed “red lines”.

The FPM, following a meeting of its leadership, said Bassil had “recalled” the leaked comments and expressed regret.

Berri and Aoun, both in their 80s, were civil war enemies. The conflict ended in 1990 when the Syrian army forced Aoun, then head of one of two rival governments, from the presidential palace and into exile.

Berri says Aoun exceeded his constitutional powers with the army promotions. Aoun says he did not.

The standoff has also strained Aoun’s political alliance with the Iran-backed Shi’ite group Hezbollah, which has longstanding ties to Amal and Berri.

MPs with Hariri’s Future Movement expressed “concerning the level of political dialogue in the country, which reached unacceptable limits, including insulting presidencies and leaders on social media sites”.

They also stressed the importance of upholding the constitution and the peace deal that ended the 1975-90 civil war.