Lebanon's newly appointed Prime Minister-designate Saad Hariri said on Saturday he would seek forming a national unity government but warned his task would be difficult.

"In line with our commitment during the election campaign in favour of a national unity government in which the main parliamentary blocs are represented ... we will begin consultations with all parliamentary blocs ...," Hariri said after meeting President Michel Suleiman.

Suleiman earlier appointed Hariri as prime minister-designate on Saturday, charging him with the task of forming a new government that would turn the page on four years of turmoil.

Suleiman issued a presidential decree designating Sunni Muslim Hariri after 86 parliamentarians in the 128-seat assembly nominated him for the post.

Hariri, who is backed by the United States and Saudi Arabia, led a political coalition to victory against Iranian-backed Hezbollah and its allies in this month's election. He is the son of statesman Rafik al-Hariri whose assassination in 2005 plunged Lebanon into the worst crisis since the 1975-1990 civil war.

Lebanon's sectarian power-sharing system reserves the premiership for a Sunni.

In a sign of the difficulties the 39-year-old leader faces in forming a cabinet acceptable to all sides, Hezbollah and its Christian allies refrained from nominating him.

Only 15 out of the minority alliance's 57 deputies backed him in two days of consultations with Suleiman, adding to support from Hariri's 71 deputies.

The main stumbling block facing Hariri is likely to be demands by militant group Hezbollah and its allies that they hold veto power in a new unity government. Hariri rejects such a veto but will seek to get the minority to participate in the government.

Hariri has been keen on securing the backing of his powerful Shi'ite rivals, who are close allies of neighboring Syria, to ensure a smooth launch for his administration.

Immediately after the June 7 election, he called for the contentious issue of disarming Hezbollah to be shelved. The group, labeled a terrorist organization by the United States, has battled Israeli forces since the early 1980s.

Hariri, who led a U.S.-backed coalition to victory over Iranian-backed Hezbollah and its allies in this month's election, met Hezbollah chief Hassan Nasrallah overnight Thursday.

A joint statement said the men, who had only met once before in three years, had held talks and discussed the outcome of the election and the possible shape of the new government.

"They also agreed on continuing discussions in the current positive calm atmosphere and stressed the logic of dialogue, cooperation and openness," it said.

Immediately after the election Hariri called for the shelving of the contentious issue of disarming Hezbollah. The group, labeled as terrorist by the United States, has battled Israel since the early 1980s.

It fought a 34-day battle against Israel in 2006, in which 1,200 people died in Lebanon and some 160 in Israel.

Pursuing justice for his father and other anti-Syrian figures assassinated since 2005 had been one of Hariri's priorities. He twice passed on the chance of becoming prime minister, preferring to give the post to his father's senior aide Fuad Siniora.

He had repeatedly accused Syria of the killings but has toned down his anti-Syrian rhetoric after the March establishment of an international tribunal to try the killers.