Geneva (AFP) - The UN special envoy for Syria, Staffan de Mistura, on Tuesday began talks with government representatives aimed at moving peace talks up a gear in Geneva, an AFP reporter said.

The meeting followed de Mistura's announcement Monday that indirect talks between the bitter foes in the almost five-year conflict had at last begun in earnest.

The main opposition umbrella group, the High Negotiations Committee (HNC), is due to meet de Mistura on Tuesday afternoon and has continued pressing for immediate progress on getting humanitarian aid into besieged towns.

It wants the bombardment of civilians by government and Russian forces to stop and for prisoners to be released, in line with a UN Security Council resolution approved unanimously in December.

In an apparent gesture of goodwill for the talks, Syria's government agreed on Monday "in principle" to allow aid into three besieged towns in Syria, including starvation-struck Madaya, the UN said.

HNC spokesman Munzer Makhous was sceptical, however.

"The regime will without doubt make some small signs. There was the announcement on Madaya... but this was designed to distract the international community's attention," he told AFP on Tuesday.

"The problem is much more vast than that. We are going to insist on all our demands being applied," he said.

Damascus says that rebels are also besieging towns, and objects to the inclusion in the HNC -- backed by Washington and Saudi Arabia -- of rebels whom it sees as "terrorists."

One of these, the HNC's chief negotiator, is Mohammed Alloush from the powerful Saudi-backed armed rebel group Army of Islam, or Jaish al-Islam, who arrived in Geneva late Monday.

The indirect "proximity talks" are due to last six months and were included in an ambitious roadmap set out in November in Vienna by the many outside powers embroiled in the conflict.

By AFP