Yemen's Shia Houthi rebel group on Sunday vowed to confront the offensive by the Saudi-led coalition and Sunni tribal fighters.
Rebel leader Abdul Malik al-Houthi condemned Saudi Arabia for interfering in Yemen's domestic affairs, and said, "We can decide our politics, form our government," according to a Xinhua report.
"We took government institutions to protect those from Al Qaeda... they asked us to withdraw from ministries and from southern provinces in order to let Al Qaeda seize them... and that will not happen," he said.
Military sources said that the Houthi leader was hiding in the mountainous regions in Yemen's north Saada province that borders the oil-rich Saudi Arabia.
Yemen's exiled President Abd-Rabbu Mansour Hadi named Prime Minister Khaled Bahah vice president last week in the Saudi capital of Riyadh.
Bahah said negotiations involving all Yemeni political parties would not be held until Hadi returned to Aden and the Houthis disarmed.
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On the same day, deadly fighting between the pro-Hadi tribal militia and Houthi gunmen erupted in the southern port city of Aden, killing at least 12 people and wounding dozens of others, medical sources told Xinhua.
A health ministry official in Aden said that "more than 290 people were killed and about 2,800 others injured, mostly civilians since the beginning of fighting in the city".
According to statistics released by Yemen's health ministry and interior ministry, over 600 people were killed and 3,000 wounded in the fighting and airstrikes in the country since mid-March.
The Saudi-led forces on Sunday launched a series of airstrikes on several Houthi-controlled military sites in the southern province of Taiz and bombed the special security forces headquarters.
Just a few hours after the bombings, fierce conflicts broke out between army units loyal to Hadi and Houthi gunmen backed by soldiers of the elite republican guard forces in many areas of Taiz, according to local security sources.
An official of Taiz local government said that the Saudi-led air raids and the street fighting left more than 18 people dead.
He said that the persistent fighting and intensified airstrikes have forced thousands of families in various cities of the Taiz province to flee.
In the al-Dhalea province on the other hand, dozens of people were either killed or injured in confrontations between pro-Hadi militia and Houthi gunmen since Sunday morning.
A tribal leader said that seven Houthi rebels were killed and 13 critically wounded in the province.
Yemen's southern provinces have witnessed a drastic escalation of violence since mid-March when fighting erupted between the Houthis and tribal militia loyal to Hadi, who is currently in Saudi Arabia after fleeing his presidential palace in Aden last month.
The fighting has caused severe shortages of food, drinking water, medicine and fuel in the country.
A coalition led by Saudi Arabia started airstrikes on Houthi targets in the Yemeni capital of Sanaa and other cities late last month, saying that the multinational action was to protect President Hadi's legitimacy and force the Houthis to retreat from cities they had seized since September 2014.