At least 7,000 people were killed in Yemen in 2014, including at least 1,200 civilians, three times the level of deaths from when the current turmoil began in 2011, according to a Yemeni think-tank's report.

It is now thought that Shia Houthi fighters are controlling about 70 percent of army's capabilities, the Abaad Centre for Strategic Studies says in a report.

During 2014 the Houthis seized more that 120 tank-type vehicles as well as other armoured vehicle and about 100 rockets during operations in 2014, the report said.

The Arabian Peninsula country has been in turmoil since 2011 pro-democracy protests forced long-ruling President Ali Abdullah Saleh to step down.

The Houthis, also known as Ansarullah, overran the capital Sanaa unopposed in September and have since advanced into mainly Sunni parts of the country.

They have been met with fierce resistance by al-Qaeda's Yemeni branch, AQAP, and Sunni tribal fighters.

The report concludes that the political transition since the rule of long-time President Ali Abdullah Saleh has failed.

On the ground, political violence continued unabated on Sunday, when a bomb explosion in Dhamar reportedly killed at least four people, including a reporter, and wounded 25 others.

A security official said the bombing targeted a gathering of Houthi supporters in Dhamar, a mainly Shia city south of Sanaa controlled by the group.

Saba, the official news agency, reported that three members of the "popular committees", a local police force created by Houthi fighters, and a reporter lost their lives in the blast.

Claiming responsibility, AQAP said on its Twitter account the explosion killed five Houthi fighters and wounded 35 others.

Series of attacks

Sunday's blast occurred three days after almost 50 people were killed when a suicide bomber targeted a religious celebration by Houthi supporters in the mainly Sunni city of Ibb.

It also came a day after the head of the Houthis threatened to take control of the oil-rich Marib province, targeted by the group since it seized Sanaa and central Yemen three months ago.

"If official authorities do not assume their responsibilities, [we] will act to support the honourable people of Marib," Abdelmalek al-Houthi said in a televised address to supporters in Sanaa on Saturday.

Elsewhere in Yemen, a senior army officer was shot by unidentified assailants, the Defence Ministry said on Sunday.

The ministry said on its news website that Colonel Hamoud Hussein al-Dharhani was killed outside his house in Ataq, a city in the southeastern Shabwa province.

Shabwa served as a stronghold of AQAP and other armed groups in recent years, who used the province's rough desert terrain to set up hideouts and training camps.

The Defence Ministry said the authorities were investigating the attack.

The killing in Ataq was the latest attack on military personnel believed to be AQAP's handiwork.

Authorities blame AQAP for the killings of between 200 and 350 senior army officers in Yemen in the past three years.