Questions remain about whether the US plans to intercept potential shipments of Iranian weapons to the Houthi rebels.
At least 69 people have been killed and 250 others wounded by explosions after Arab coalition fighter jets hit an arms depot near the Yemeni capital Sanaa, according to medical officials.
Residents said that explosions at a military base at Mount Noqum, on the city’s eastern outskirts, lasted until mid-day on Tuesday after coalition jets struck the depot late on Monday.
An official told AFP news agency that most of the people killed and wounded were civilians.
Medics on the ground had given an earlier toll of five killed and 20 wounded.
The air strikes set off huge explosions that sent debris crashing into a residential area at the foot of the mountain, witnesses said.
Elsewhere, in Taiz, shelling blamed on Iran-allied Houthi fighters killed at least 10 people.
A five-day pause in the coalition bombing campaign was due to start at 11pm local time [20:00 GMT] on Tuesday to allow deliveries of desperately needed relief supplies.
Adel al-Jubeir , the foreign minister of Saudi Arabia, which is leading the Arab coalition, was quoted as saying on Monday that the truce might be extended if aid deliveries succeeded and if the Houthis and their allies did not engage in hostile activities.
Tuesday’s air raids came as Iran said it would send a cargo ship full of aid to the Yemeni port of Hodaida, held by Houthi fighters.
Iranian warships will escort the vessel, a naval commander was quoted as saying by Iran’s state news agency IRNA.
“The 34th fleet, which is currently in the Gulf of Aden, has special responsibility to protect the Iranian humanitarian aid ship,” Admiral Hossein Azad said, referring to a destroyer and support vessel in international waters off Yemen.
Earlier on Tuesday, the new UN envoy to Yemen arrived in Sanaa in advance of the proposed truce.
Ismail Ould Cheikh Ahmed said he would hold talks on restarting the political dialogue which collapsed when President Abd-Rabbu Mansour Hadi escaped from Sanaa in February.
“We are convinced that dialogue is the only way to solve the Yemeni problem,” the Houthi-controlled Saba news agency quoted him as saying.
“Any ceasefire and any halt on the military operations is supported by Iran to help the victims of this war which are innocent children and women,” he said.
The conflict in Yemen has killed more than 1,400 people – many of them civilians – since March 19, according to the UN, and the country of some 25 million has endured shortages of food, water, medicine and electricity as a result of a naval, air and land blockade.