Saudi ruler King Abdullah meets Syrian leader Bashar al-Assad on Thursday to try to ease tensions in Lebanon, capitalising on an apparent weakening in Iran's position after a round of tough new sanctions.

The monarch will hold talks with Assad in Damascus before heading to Beirut where he will meet his ally Premier Saad al-Hariri, President Michel Suleiman and pro-Western Lebanese political leaders, Saudi officials said.

The monarch hopes to convince Assad to accompany him to Beirut from Damascus, Lebanese officials say, although Syria has not confirmed that Assad will oblige.

The king is expected to press Assad to use his influence over Lebanon's Iranian and Syrian-backed Shi'ite Muslim group Hezbollah to discourage it from heightening tensions, especially between Hezbollah and Sunni political leaders like Hariri.

Hezbollah leader Sayyed Hassan Nasrallah has condemned the U.N. investigation into the 2005 killing of Saad's father, former premier Rafik al-Hariri, saying he expected it to indict many Hezbollah members.

Sunni Muslim Saudi Arabia has been trying to persuade Syria to loosen its alliance with Iran and adopt a more Arab-focused foreign policy, with Saudi officials hinting at financial aid for Syria and a resumption of investment there in return.

Shi'ite Iran's growing influence in the Arab region since the U.S.-led invasion of Iraq in 2003, and its links to Syria, Lebanon's Hezbollah, Hamas and various groups in Iraq, have alarmed U.S.-allied powers such as Egypt and Saudi Arabia.

"The king appears keen to deal with concerns that recent tensions could escalate if the (U.N.) court takes some decisive action in the Hariri murder case," said Khalid al-Dakhil, a prominent Saudi political writer.

"The visit also aims at ascertaining the regional understandings Syria has with Saudis, Turks, the French .... to keep Lebanon stable and stay away from Lebanese internal political wranglings."

Indictment of Hezbollah members for Hariri's killing would put severe strains on Lebanon's unity government, which is led by Hariri's son Saad and includes Hezbollah ministers.

WAR THREAT

President Michel Suleiman held four days of talks with political leaders earlier this month to try to calm tensions, which echo the deep divisions that threatened to ignite a new civil war in 2008.

Before the Syrian leg, King Abdullah will on Wednesday meet Egyptian President Hosni Mubarak, who has been rumoured to be seriously ill.

A Riyadh-based Western diplomat said the visit by the Saudi monarch to Beirut would send a signal of stability. "It's brave of him to go there amid the tense political context. It shows that the kingdom is leading the pan-Arab regional diplomacy that takes the initiative," the diplomat said.

Extended sanctions by the United Nations against Iran in June seem to have encouraged moderate Arab states, including Saudi Arabia, to be bold in addressing the threat of instability in Lebanon.

"The tougher sanctions on Iran have a negative impact on Hezbollah, and Hezbollah is not happy about them. But Syria has never abandoned Hezbollah and will not abandon it. But its perspective and calculations have changed," Dakhil said.

Saad al-Hariri, who initially blamed Syria for his father's death, has since tried to ease tensions with Damascus and has made several trips to meet Assad. Syria has denied any involvement in Hariri's killing.

Damascus, whose allies such as Hezbollah have effective veto power in the government, had re-set relations with Lebanon after improving ties with Saudi Arabia.

Rafik al-Hariri's killing angered Riyadh but Saudi Arabia and Syria appear to set aside their differences last year with the aim of healing divisions between their allies in Lebanon.