DUBAI (Reuters) - A frigate attacked a fishing boat off Yemen’s Red Sea port of al-Khoukha, killing 18 fishermen on Tuesday, relatives said. The Saudi-led coalition fighting the Houthi group denied reports that it had carried out the attack.

Members of the fishermen’s families told Reuters only one person survived when a warship attacked the boat.

The Saudi-led coalition denied attacking the boat and said an unknown vessel opened fire on the fishermen, killing 17.

“The command of the coalition forces assures that what some media reported about the coalition’s navy targeting fishing boats off al-Khoukha port is baseless,” the coalition spokesman, Colonel Turki al-Malki, said in a statement.

He accused the Houthis of carrying out similar attacks in the past.

The coalition led by Saudi Arabia and the United Arab Emirates intervened in Yemen in 2015 to restore the exiled government of president Abd-Rabbu Mansour Hadi, but the Houthis still control most populated areas, including the capital Sanaa and the port city of Hodeidah, 120 km (75 miles) along the coast from Al-Khoukha.

Heavy fighting resumed in Hodeidah last week as pro-government forces launched an assault to retake the city.

Al-Khoukha port is under the control of the UAE military, which drove out the Houthis last December and where they built a military base used in the battle for Hodeidah.

Al-Malki said the coalition was investigating the incident and had gathered information from fishermen present in the area and the one who survived the attack.

Coalition-backed Yemeni forces last week said they seized the main road linking Hodeidah to Sanaa as part of a strategy to isolate the two cities, both held by the Houthis, who denied the claim.

U.N. special envoy Martin Griffiths left Sanaa on Tuesday after a three-day tour aimed at convincing the Houthis to send representatives to Geneva for consultations that could lead to a peace agreement.

“Constructive meetings in Sanaa with Ansarullah (Houthi) leadership ... made progress on ways to resume consultations and confidence building measures, including release of prisoners, economic situation and re-opening of Sanaa airport,” Griffiths’ office said on Twitter.

He will be in Riyadh on Wednesday, his office added.

The Houthis did not show up in Geneva for talks earlier this month after they said their plane should be provided by a neutral party and should not be inspected by the coalition. They also asked to evacuate some of their wounded to Oman or Europe.