GENEVA (AFP) - Syria's largest mainstream opposition group said Friday (Jan 29) that it would attend United Nations-led peace talks in Switzerland, easing fears that it would boycott a process aimed at ending the tangled civil war.

The Saudi-backed High Negotiations Committee (HNC) said it would "take part in the political process to test the seriousness of the other side through discussions with the UN team", after four days of suspense over whether it would join.

Despite Western pressure to attend, the HNC had previously said it would not take part in the Geneva talks without an agreement on relief reaching hundreds of thousands of people stuck in besieged Syrian towns.

A senior HNC delegate told AFP the Committee will send "about 30, 35 people" to the talks, which got under way on Friday (Jan 29) in the biggest political push yet to end Syria's almost five-year war.

In a tweet, however, the HNC stressed that the group would be there "to participate in discussions with the @UN, not for negotiations".

Backed by external powers embroiled in Syria's war, the talks are seeking to end a conflict that has killed more than 260,000 people and fuelled the meteoric rise of the extremist Islamic State group.

US Secretary of State John Kerry, France and Saudi Arabia, where the HNC is based, welcomed the late decision to send a delegation.

Representatives from the regime of Syrian President Bashar al-Assad arrived earlier on Friday (Jan 29) for their first meeting with UN special envoy Staffan de Mistura.

The 16-member delegation met with the UN mediator for nearly three hours, and left the body's headquarters without speaking to media.

De Mistura said his preliminary talks with the HNC could happen on either Saturday (Jan 30) or Sunday (Jan 31), telling reporters they would have "some work... certainly on Monday".

The HNC had previously demanded an end to bombardments of civilians, as well as an agreement on humanitarian aid to ease suffering in besieged towns, before agreeing to take part in the talks.

And the group asked for "clarifications" after the UN invited other opposition figures who are thought to have closer ties to Moscow and limited influence on the ground.

The HNC and its Saudi and Turkish backers have also objected to the participation of Syrian Kurdish groups that have made key advances against Islamic State in Iraq and Syria (ISIS) extremists in northern Syria in recent months.

Asaad al-Zoabi, head of the HNC delegation, told Sky News Arabia the group had received the guarantees it wanted from Washington and Saudi Arabia, adding the delegation would arrive Saturday (Jan 30) evening or Sunday (Jan 31) morning.

The HNC did not announce who it would send to Geneva, but it had earlier said that a future delegation would include women and members of religious minorities.

In a controversial move, the alliance has named Mohammed Alloush, member of the Army of Islam rebel group, as its chief negotiator.

Formed in December after months of Saudi efforts, the HNC is the largest alliance of mainstream opposition groups in Syria.

Syria's civil war, which has been raging for almost five years, has destabilised the already restive Middle East and drawn in regional powers like Saudi Arabia, Iran and Turkey but also the United States and Russia.

It has also forced millions of Syrians from their homes, many of them into neighbouring states and further afield, causing a major political headache for the European Union which received more than one million migrants in 2015.

The negotiations would not be face-to-face between the regime and its opponents. Instead they are "proximity talks" where go-betweens shuttle between the different participants.

They are part of an ambitious plan launched in Vienna in November by a raft of key actors including Russia, the United States, Gulf states, Iran and Turkey that foresees elections within 18 months.

Russia, however, which has helped Assad's regime make inroads against rebels with air strikes since September, says Kurdish involvement is essential.

Iranian President Hassan Rouhani, whose Shi'ite country also backs Assad and is at daggers drawn with Sunni regional rival Saudi Arabia, said during a visit to Paris on Thursday (Jan 28) that he hoped the process would be successful.

"But I would be surprised if they succeed very quickly because in Syria there are groups who are at war with the central government and also amongst themselves," French media quoted him as saying.