A Moroccan F-16 warplane taking part in a bombing campaign in Yemen led by Saudi Arabia has gone missing, the Moroccan Royal Armed Forces has said in a statement.

Morocco announced its backing of Saudi Arabia since the beginning of the military offensive in March, and has had F-16 warplanes stationed in the United Arab Emirates (UAE), the Reuters news agency reported on Monday.

"One of the F-16s of the Royal Armed Force made at the disposal of the coalition led by Saudi Arabia to restore the legitimacy in Yemen went missing on Sunday at 6pm local time," FAR's statement carried by the Moroccan state news agency MAP said.

The pilot of a second jet in the same squadron could not see if the pilot had ejected, it said. An investigation is under way, it added.

Backed by the United States, the coalition has been conducting air raids against the Houthi fighters since March 26 nearly a month after the rebels toppled the government of President Abd-Rabbu Mansour Hadi.

Hadi, who was backed by the West, fled to Saudi Arabia in February and requested the regional allies for intervention to oust the Houthis, who have taken control of the country with the help from forces loyal to former President Ali Abdullah Saleh.

Saleh's home bombed

The incident on Sunday night came hours after the former president formally announced an alliance with Houthi fighters for the first time, after the Arab coalition launched two air strikes on his home in the capital, Sanaa.

Saleh, who was forced to step aside in 2012 following a year of deadly nationwide protests against his three-decade rule, escaped unharmed after the attacks early on Sunday.

The former president, who was accused of siding with Houthi fighters, was later defiant against the Arab coalition.

"You should continue carrying your arms, ready to sacrifice your lives in defence against these belligerent attacks," Saleh said, addressing Houthis after the attack.

"I can describe this aggression as an act of cowardice.

"If you are brave enough, come and face us on the battlefield, come and we will be at your reception. Shelling by rockets and jet fighters cannot enable you to achieve any of your goals."

Humanitarian ceasefire

Saleh's comments came after Houthi fighters released a statement that they would deal "positively" with any efforts to lift the suffering of the Yemeni people.

The declaration was seen as a sign that they could accept a five-day humanitarian ceasefire proposed by Saudi Arabia.

The Houthis' political council said on Sunday that they would like to see humanitarian aid delivered to the Yemeni people as soon as possible.

Houthi sources told Al Jazeera that the group would never accept talks to be held in Riyadh, or any other nation involved in the Arab coalition.

Adel al-Jubeir, the Saudi foreign minister, announced a proposal on Thursday for a five-day ceasefire to facilitate humanitarian aid to civilians, but only on the condition that the Houthis also halt the fighting.