CAIRO/ADEN, May 12 (Reuters) - Saudi-led air strikes hit the rebel-held Yemeni capital Sanaa on Tuesday hours before a five-day humanitarian truce was set to begin, and Washington cautioned against "provocative actions" after Iran dispatched a cargo ship to Yemen.
The United States said it was tracking Iranian warships accompanying the vessel bound for the port of Hodaida, and urged Iran instead to use a U.N. distribution hub in Djibouti to provide help to people in the war-damaged Arabian Peninsula country.
"We're certainly tracking this convoy closely," U.S. State Department spokesman Jeff Rathke told a daily briefing. "We would discourage any provocative actions."
Iran is an ally of the Houthi movement, Yemen's most powerful political faction which is under attack by a Saudi-led coalition which accuses the group of toppling the country's rightful government.
Iranian warships will escort the vessel, a naval commander was quoted as saying by 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.
In the latest violence, warplanes bombed targets in the northern province of Hajja near the border with Saudi Arabia, killing 20 people, most of them civilians, residents said.
Looking to prepare for the truce and jumpstart stalled political talks among Yemen's civil war factions, the new U.N. envoy to the country arrived in Sanaa, saying fighting would not resolve a conflict that crosses ethnic and religious faultlines.
A Shiite fighter known as a Houthi inspects a house destroyed by a Saudi-led airstrike in Sanaa, Yemen, Monday, May 11, 2015. (AP Photo/Hani Mohammed)
"We are convinced there is no solution to Yemen's problem except through a dialog, which must be Yemeni," the envoy, Mauritanian diplomat Ismail Ould Cheikh Ahmed, was quoted as saying by the local Saba news agency.
Seeking to restore exiled President Abd-Rabbu Mansour Hadi, an alliance of Gulf Arab nations has since March 26 been bombing the Iranian-backed Houthi militia and allied army units that control much of Yemen.
Backed by Washington, top oil exporter Saudi Arabia worries that the Shi'ite Muslim Houthi rebels are a proxy for what they see as moves by arch-rival Iran to expand its sway in their backyard.
Saudi-led air strikes on a rocket base in Sanaa on Monday killed 90 people and wounded 300, a local official was quoted as telling Saba. If confirmed, the death toll would be among the highest in a single bombing incident throughout Yemen's war.
Sanaa residents said there were three air strikes on a base for army contingents aligned with the Houthis in the north of the capital on Tuesday, sending up a column of smoke.
The ceasefire was set to take effect at 11 p.m. (2000 GMT) to allow the shipment of food and medicine to the country, which aid groups warn faces a humanitarian catastrophe.
Saudi Foreign Minister Adel al-Jubeir was quoted as saying on Monday that the truce in Yemen may be extended if "(aid deliveries) succeeded and if the Houthis and their allies don't engage in hostile activities."
Smoke rises from a house of former Yemeni president Ali Abdullah Saleh after a Saudi-led airstrike in Sanaa, Yemen, Sunday, May 10, 2015. (AP Photo/Hani Mohammed)
Adrian Edwards, a spokesman for U.N. refugee agency UNHCR, said planes were poised to take off from Dubai in the United Arab Emirates bearing 300 tonnes of sleeping mats, blankets and tent material.
"The UNHCR is making final preparations for a huge airlift of humanitarian aid into Yemen's Sanaa, to take place over the next days if today's proposed ceasefire comes into effect and holds," he told a briefing in Geneva.
As the ceasefire neared, witnesses said the Saudi-led alliance bombed Houthi positions in the southern port of Aden, where local armed groups were still fighting the rebels.
Locals said four Aden residents were killed in Houthi shelling, while four anti-Houthi militiamen operating a tank were killed in an Arab air strike - one of the first reported incidents of friendly fire since the campaign began.
On Monday, the Houthis and Saudi forces exchanged heavy artillery fire along the two countries' rugged desert border.
As of Wednesday, the U.N. agency OCHA said 1,527 people have died in the conflict, among them 646 civilians, and 6,266 have been wounded. (Additional reporting by Sam Wilkin in Dubai and Stephanie Nebehay and Tom Miles in Geneva; Writing by Noah Browning and William Maclean; Editing by Crispian Balmer and Dominic Evans)