ADEN, Yemen

 At least 20 people were killed and 70 others injured in clashes between Houthi militants and vigilante tribesman who back Yemeni President Abd Rabbuh Mansour Hadi in the southern province of Aden, medical sources said.

According to the sources, most of the victims were civilians who  were caught in crossfire over the past 24 hours.

Eyewitnesses told The Anadolu Agency that heavy clashes erupted early Thursday when Shiite Houthi militants tried to sneak into Crater district in Aden. The attempt was repelled by the pro-Hadi vigilantes stationed in the area, they added.

In response, the Houthis shelled several residential buildings in the neighborhood, leaving several civilians dead, the witnesses told AA.

Deadly clashes were also reported in the northern districts of Mansoura, Dar Saad, and Sheikh Othman.

Aden is the main stronghold of embattled Hadi who fled to Saudi capital Riyadh late last month after Houthi militants struck his residence in the city.

Since March 25, Saudi Arabia and its Arab allies have been pounding Houthi positions across Yemen.

Riyadh says its anti-Houthi campaign comes in response to Hadi's appeals to "save the [Yemeni] people from the Houthi militias."

The United States, for its part, is providing logistical and intelligence support to the ongoing anti-Houthi offensive.

The Houthis, for their part, consider the "Saudi-American onslaught" a "blatant violation of Yemeni territory."

Yemen has remained in turmoil since last September, when the Houthis overran capital Sanaa, from which they have since sought to extend their influence to other parts of the fractious country.

Some Gulf States accuse Shiite Iran of supporting Yemen's Houthi insurgency.