The UN special envoy to Yemen, Ismail Ould Cheikh Ahmed, said on Sunday that progress has been made in peace talks over the Yemen war.

The UN special envoy to Yemen, Ismail Ould Cheikh Ahmed, said on Sunday that progress has been made in peace talks over the Yemen war.

In a news conference, the UN envoy said he was optimistic about achieving a peaceful settlement in the war-torn country, but admitted "difficult matters" remain unresolved.

Ould Cheikh Ahmed said some progress had been achieved in the talks which began on April 21.

"Now, we have an opportunity to reach a peaceful settlement... the progress we have made on some points makes us optimistic," he told the news conference in the Kuwaiti capital where the UN-sponsored talks has been talking place.

"But there remains some difficult matters... the problem is reaching a clear political agreement."

But the envoy declined to provide details on the progress made other than an agreement in principle to free 50 percent of prisoners and detainees before the start of the Muslim fasting month of Ramadan in the first week of June.

Yemen has been since March 26, 2015 under brutal aggression by Saudi-led coalition.

Thousands have been martyred and injured in the attack, with the vast majority of them are civilians.

Riyadh launched the attack on Yemen in a bid to restore power to fugitive Hadi who is a close ally to Saudi Arabia.