Saudi-led air strikes on a missile depot in Yemen's rebel-held capital Monday sparked explosions that left at least 18 people dead and 300 wounded, flattening houses and shaking faraway neighborhoods.

Many more people were feared to have been killed after two strikes hit the hilltop depot, leaving a trail of destruction in the Fajj Attan area of Sanaa which was covered in thick clouds of smoke.

A coalition of Sunni Arab nations led by Saudi Arabia launched the air campaign against the Huthi Shiite rebels last month, vowing to restore the authority of President Abedrabbo Mansour Hadi, who fled to Riyadh as the militiamen advanced on his southern refuge of Aden.

Riyadh has accused Iran, the main Shiite power, of backing the rebels and fears a Tehran-friendly regime taking control of the country on its southern border.

Monday's strikes on Sanaa triggered a series of blasts that sent shockwaves across the city, leaving cars mangled, buildings gutted and streets completely scattered with debris.

Fires broke out at the targeted missile base and a nearby petrol station, witnesses said, and the scorching heat could be felt from a distance.

Civilians were seen emerging from their shattered homes in the aftermath, some of them carrying suitcases and apparently stunned at the scale of the destruction outside.

Medics at four hospitals in the capital said at least 18 civilians were killed and some 300 others wounded.

The hilltop base belongs to the missile brigade of the elite Republican Guard, which remained loyal to former president Ali Abdullah Saleh who has been accused of siding with the Huthi rebels in their fight against the government.

The Huthis have seized control of large parts of the Arabian Peninsula nation, including Sanaa, and fought fierce battles with pro-government forces.

The Saudi-led coalition says it has carried out more than 2,000 strikes since the start of the campaign, gaining complete control of Yemeni airspace and knocking out rebel infrastructure.

But its spokesman, Brigadier General Ahmed al-Assiri, gave no comment about Monday's blasts in Sanaa during his daily media briefing.

Fighting continued in the south between advancing rebels and local fighters who have sided with Hadi. Eleven rebels and five southern fighters were killed in Huta, the provincial capital of Lahj, the military said.

- Iran mediation rejected -

The U.N. says the conflict has left hundreds dead and thousands wounded, and there has been increasing concern of a huge humanitarian crisis.

Calls have been growing for peace talks, but authorities on Monday rejected an Iranian offer of mediation.

"Any mediation effort coming from Iran is unacceptable because Iran is involved in the Yemen issue," said Yemeni Foreign Minister Riyadh Yassin.

"The Huthis and Saleh forces must withdraw from all cities and villages of Yemen, including Sanaa and Aden, return to (their northern stronghold of) Saada as civilians, and lay down their arms," he said.

"After that we can talk about dialogue and a political solution. But now there is no room for negotiations."

The exiled authorities was boosted Sunday when the commanders of 25,000 troops in Hadramawt province, the country's largest and on the border with Saudi Arabia, expressed their support for Hadi and his "constitutional legitimacy."

- 'Will never give in' -

But rebel leader Abdulmalik al-Huthi vowed his forces would never surrender.

"Our Yemeni people will never give in -- it will resist in the face of the savage aggression," Huthi said in televised statement on Sunday.

He promised to fight back using "all means and options" and said Riyadh "has no right to interfere" in the country.

Huthi also slammed as "unfair" a U.N. resolution imposing an arms embargo on the rebels and demanding that they return to their highland stronghold.

But in what will be seen as another welcome sign for Hadi, Saleh -- forced out after a 2011 Arab Spring-inspired uprising -- on Sunday welcomed the resolution as a "positive" step, with his party backing calls for a ceasefire and U.N.-mediated talks.

Yemen has long struggled with deep tribal divisions and an insurgency by Al-Qaida in the Arabian Peninsula (AQAP), considered by Washington as the jihadist network's most dangerous branch.

Al-Qaida militants have taken advantage of the chaos to seize territory including an army camp in Hadramawt, an airport and provincial capital Mukalla.

On Monday, a U.S. drone killed five al-Qaida suspects in a raid that struck two vehicles in Saeed, in Shabwa province.