UN-backed peace talks to end Yemen's civil war resumed on Wednesday after they were suspended by the Yemeni government for three days in protest at a Houthi assault on a military base near the capital Sanaa.

Buttressed by a truce which had been largely holding since April 10, the talks in Kuwait had been inching ahead before their pause and the Houthis said Saudi Arabia had on Saturday released 40 Yemeni prisoners.

UN special envoy to Yemen Ismail Ould Cheikh Ahmed tweeted a picture of delegates representing the main warring sides sitting around a U-shaped table and said talks on Wednesday would focus on cementing the shaky ceasefire.

The Iran-allied Houthis and Yemen's Saudi-backed exiled government are trying to broker a peace via talks in Kuwait and ease a humanitarian crisis in the Arabian Peninsula's poorest country, where the conflict has drawn in regional powers and killed at least 6,000 people.

A civil war in Yemen escalated when an armed push by the Houthis cast the government into exile on March 26 last year.

Fearing the group was a proxy for Iran, Saudi Arabia mustered an alliance of mostly Gulf Arab countries to push the group back but still appears far from beating the Houthis out of Sanaa.

Human Rights Watch on Wednesday urged participants in the talks to allow international investigations of alleged war crimes by all sides "which have not been investigated nor have resulted in any redress for victims of unlawful attacks".

The group cited air strikes on civilian areas by the Saudi-led coalition backing the government and "indiscriminate" shelling and use of landmines by the Houthis.

"The parties around the negotiating table have an obligation to ensure that the violations against civilians are properly investigated and appropriately punished," HRW deputy Middle East director said in a statement.