Artillery shelling in Aden has killed 26 people, medical officials have said, as Houthi fighters and forces loyal to Yemen President Abd-Rabbu Mansour Hadi battled over control of the southern port city.

The deaths on Tuesday came as Saudi-led coalition fighter planes continued raids on Houthi positions, killing dozens across the country.

For the first time since the coalition operation began, jets bombed renegade troops in the Shia-populated city of Dhamar, a stronghold of the Houthis south of the capital Sanaa.

Huge blasts were heard overnight in Sanaa when coalition forces hit a missile depot belonging to the renegade Republican Guard, which is loyal to former President Ali Abdullah Saleh.

The blast rocked the southwestern district of the capital with flames billowing from the site were seen by residents across most of the city.

Early in the morning, air strikes targeted two camps held by Houthi fighters and allied Republican Guard soldiers in the southern town of Al-Dali. Columns of smoke rose from the area, witnesses told the AFP news agency.

At least 10 people were killed and 32 wounded when a Saudi-led airstrike hit a gas tanker and oil pumps in Ibb province, in central Yemen. Air strikes also targeted the camp of the 131 Infantry Brigade in Saada and Houthi positions in the cities of Taiz and Hodeidah.

Over the past few days, air strikes have targeted at least nine of Yemen's 21 provinces in an attempt to prevent the Houthis from reaching Aden

The strikes came a day after at least 40 people were killed when a refuge camp in Hajjah, northwest of Sanaa, was bombarded, with conflicting reports on who was being targeted.

A number of sources said an airstrike was responsible for the deaths at al-Mazraq camp, but Yemen's foreign minister, Riyadh Yasin, insisted it was caused by Houthi artillery fire.

Pablo Marco, the manager of the Doctors Without Borders (MSF) programme in the Middle East said: "It was an air strike," adding that dozens of Yemenis were injured.

"There are a lot of civilians there, I do not know if there are Houthi fighters inside the camp, but most of the people are civilians," Marco told Al Jazeera.

However, witnesses told the AP news agency that while the camp used to house people displaced by an earlier conflict that ended five years ago, it was now occupied by Houthi forces and that most of those killed were fighters.

UN human rights staffers told the AP they verified at least 19 civilians were killed when airstrikes hit the camp, with at least 35 wounded, including 11 children.

Al Jazeera's Hashem Ahelbarra, who has reported extensively from Yemen, said thousands of displaced Yemenis had been living at camps such as Al-Mazraq since 2004, after being driven from their homes by an offensive launched by former President Ali Abdullah Saleh against the Houthis.