KATHMANDU (AFP) - Sushil Koirala was sworn in as Nepal's prime minister on Tuesday, after winning the backing of fellow legislators and tasked with steering the strife-torn Himalayan nation towards stability.

Mr Koirala, head of the country's biggest political party the Nepali Congress, took his oath before President Ram Baran Yadav during a ceremony at his office.

"I, Sushil Koirala, in the name of God, pledge that I will be committed and honest to the nation and its people to fulfill my duty as prime minister," said Mr Koirala, reading the oath, as officials and dignitaries looked on.

On Monday, the silver-haired bachelor easily won a vote of legislators in the constituent assembly, which was elected last November in only the second national polls since the end of a civil war in 2006.

After the vote, Mr Koirala pledged to steer through a long-delayed new constitution within a year, to complete the nation's stalled peace process.

"We will deliver the constitution through agreement, unity and reconciliation,"

Mr Koirala, who was once jailed over the hijacking of a plane in India, told reporters after the vote.

Mr Koirala's elevation is also expected to pave the way for the formation of a new coalition government charged with ending a prolonged political crisis that has crippled Nepal's economy.

The Nepali Congress party, which won the most seats at the polls, gained the support of the Unified Marxist-Leninist party on the weekend to form a coalition government, although details have not yet been worked out.

Since Nepal's first post-war elections in 2008, five prime ministers have served brief terms, the country has had no leader for long periods, and the constituent assembly has been perpetually deadlocked.

The first version of the assembly, dominated by the one-time rebel Maoists, finally collapsed in May 2012 after failing to agree on a constitution and complete the peace process.