NEW YORK - Iran proposed a four-point peace plan for Yemen on Friday that calls for an immediate ceasefire and the formation of a unity government.

In a letter sent to UN Secretary-General Ban Ki-moon, Iran's Foreign Minister Mohammad Javad Zarif urged the New York-based body to get more involved in ending the "senseless" airstrikes, referring to the Saudi Arabian-led air campaign that has pounded Shiite Houthi positions in Yemen since 25 March.

The impoverished Arab country has been in turmoil since last September when Houthi rebels seized the capital Sanaa and have advanced to other parts of the country.

The current conflict is seen in some circles as a proxy war between majority Sunni Saudi Arabia and predominantly Shiite Iran.

"It is imperative for the international community to get more effectively involved in ending the senseless aerial attacks and establishing a ceasefire, ensuring delivery of humanitarian and medical assistance to the people of Yemen and restoring peace and stability to this country through dialogue and national reconciliation without pre-conditions," said Zarif's letter, which was obtained by Reuters.

The letter said terrorist groups were "gaining strategic foothold in Yemen aided by the foreign aerial campaign".

Iran’s plan calls for the restoration of a "Yemeni-led" national dialogue among all factions, and says a ceasefire will ensure access to humanitarian aid for the Yemeni population.

“This critical situation is escalating and the humanitarian crisis in Yemen is approaching catastrophic dimensions," read Zarif's letter.

"It may result in further exacerbation of the already tense circumstances in a region that has been plagued by one of the most barbaric types of extremism and multi-pronged vicious campaign of foreign-backed terrorists," it added.

The UN estimates more than 731 victims have been killed in Yemen since 19 March.

On Thursday, the UN chief also called for an immediate ceasefire to allow for lifesaving humanitarian aid and the restoration of peace in the country.

The UN envoy for Yemen, Jamal Benomar, resigned earlier in the week, saying he wanted to move on to a new assignment, but diplomats confirmed that he had lost the support of Yemen's exiled president and Gulf countries.

Saudi Arabia and its neighbours accuse Benomar of being duped by the Houthis who took part in peace negotiations as they pushed their offensive.

The UN humanitarian affairs agency, OCHA, on Friday appealed to international donors to provide $274 million in order to provide aid for 7.5 million Yemenis - more than 30 percent of the population - who are in need of urgent humanitarian assistance.

As many as 12 million Yemenis are food insecure, and at least 150,000 have been displaced, according to the UN.