Warplanes from the Saudi-led Arab coalition have launched heavy raids against rebel positions in seven Yemeni provinces, witnesses and military sources said Wednesday.

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 Shiite Huthi rebels, 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 the Iran-backed Huthis 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.

The rebels 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 UN figures, and almost 80 percent of the population -- 20 million people -- are in need of urgent humanitarian aid.

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