Two roadside bombs exploded one after the other on a busy road in the Yemeni capital on Thursday wounding 20 people, the interior ministry said.

The twin blasts were on Al-Rabat Street where the explosive devices had been hidden among piles of garbage.

Unidentified gunmen shot dead on Tuesday a Yemeni air force officer in the capital, the second killing of its kind in less than 24 hours, a military official said.

Colonel Ali al-Dailamy died instantly after he came under fire from gunmen near the military hospital in Sanaa, the official said, adding that the assailants managed to flee.

An unidentified gunman killed a Yemeni air force officer in the capital on Monday, a military official said.

An assailant riding a motorbike opened fire on Colonel Abdulwahab Azzan as he was driving back from Al-Dailamy air base, 20 kilometers (12 miles) north of Sanaa, the official said.

Yemeni Prime Minister Mohammed Basindawa escaped unharmed as gunmen opened fire on his convoy in the capital on Saturday, a security source said.

"Four unknown gunmen opened fire on the prime minister's convoy in central Sanaa as he was heading home," the source told Agence France Presse, adding that no one was hurt in the attack.

A powerful blast struck a bus transporting Yemeni air force personnel to their base in Sanaa on Sunday, killing at least six of them, a security official said.

A bomb planted on the bus exploded while the vehicle was traveling on the road leading to Sanaa international airport, which is adjacent to the base, the official said.

A bomb hidden in a plastic bag exploded at a checkpoint in the Yemeni capital Sanaa on Saturday, killing three policemen and wounding a fourth, a security services official said.

The device was planted near a police checkpoint in the north of the capital and detonated as the policemen opened the bag to check its contents, the official added.

Tribal gunmen kidnapped on Monday a Swiss man working for the International Committee of the Red Cross in southern Yemen, a local pro-government militia leader said.

The gunmen who belong to Al-Marakisha tribe kidnapped the man in the city of Jaar, in Abyan province, said Hussein al-Wahayshi, a local commander of the Popular Resistance Committees.

A Yemeni military aircraft ploughed into a building in a residential neighborhood of Sanaa on Tuesday killing at least nine people, medics and witnesses said.

The pilot was killed when the plane crashed near Change Square in eastern Sanaa, while at least eight civilians died on the ground, the sources said.

A U.N. Security Council delegation on Sunday began a brief visit to Yemen in a clear boost to President Abdrabuh Mansur Hadi aimed at helping to iron out problems hampering national reconciliation talks.

The delegation, which includes the head and members of the top body as well as United Nations special envoy Jamal Benomar, went straight into a meeting with Hadi, state television said.

Three U.S. drone strikes killed nine suspected members of Al-Qaida in the Yemen province of Marib, a tribal chief and witnesses said on Sunday.

One raid late on Saturday targeted a vehicle transporting four suspected members of the jihadist network in Wadi Abida, east of the city of Marib, 170 kilometers (110 miles) east of Sanaa, the tribal source said.