The attacks that began overnight and continued Wednesday were the most intensive since the beginning of the Muslim fasting month of Ramadan last week, witnesses said.

Positions were targeted in the northern region of Saada, which is the main stronghold for the Iran-backed Houthi militia, as well as Hajja on the border with Saudi Arabia, residents said.

The warplanes also raided positions in the western province of Hodeida, and the provinces of Baida, Daleh, Lahj and Aden, in the south.

The targets included Houthis as well as troops loyal to former president Ali Abdullah Saleh, who has allied himself with the rebels against the government of exiled President Abedrabbo Mansour Hadi.

The warplanes hit rebels near the airport of Aden, where heavy fighting continues between rebels and southern fighters allied with Hadi, military officials loyal to Hadi said.

Four civilians, including two women, were killed in clashes in Aden, an official said.

Houthis who overran the capital Sanaa in September have since expanded their control to several other regions. In March they advanced on Aden, where Hadi had taken refuge before fleeing to Saudi Arabia.

The Saudi-led coalition launched a bombing campaign against the rebels late March in support of Hadi.

More than 2,600 people have been killed in Yemen since March, according to U.N. figures, and almost 80 percent of the population — 20 million people — are in need of urgent humanitarian aid.

U.N.-brokered peace talks between the rebels and government officials ended in Geneva last week without agreement.

U.N. appeals for ceasefire

Meanwhile, the U.N. envoy for Yemen on Wednesday urged warring sides to agree to a ceasefire as fighting pushed the poor Arab country closer to famine and deeper into humanitarian crisis.

Mauritanian diplomat Ismail Ould Cheikh Ahmed said a ceasefire was a priority after reporting to the Security Council on his failed peace talks in Geneva last week.

“It is imperative for all the parties — and for me everybody is responsible — to find a truce,” the envoy told reporters.

He called for the ceasefire to take hold before the end of Ramadan on July 17.

“We are one step away from famine,” said Ould Cheik Ahmed. “We want to really find a way to lessen the suffering of the population.”

Some 80 percent of Yemen’s population — 21 million people — are in need of humanitarian aid and one million people have been displaced in the fighting, the envoy said.

A recent outbreak of dengue fever and fears that polio will return to the country are compounding concerns about the humanitarian emergency in Yemen.

The U.N. envoy said a ceasefire would provide for the withdrawal of militias from the cities and set up a monitoring mechanism to report on possible violations.

Ould Cheikh Ahmed stressed there was no military solution to the conflict and said he would press on with his efforts to achieve a ceasefire and a return to political talks.

No date was announced for a new round of talks, but the envoy is continuing consultations with all sides.

A Security Council diplomat separately said it was essential that Saudi Arabia lift its maritime blockade to allow life-saving supplies to reach Yemen.

“Yemen is so dependent on imports for food, health services, fuel,” said the diplomat, who asked not to be named.

“There must be some lifting of this blockade so that ships can get through.”

The diplomat also described prospects for a new round of political talks as “bleak.”