Al-Qaeda gunmen Monday launched spectacular attacks on two army posts in south Yemen, killing at least 20 soldiers, apparently to avenge the death of a top militant in an air raid, a military official said.

Jihadists attacked the military posts outside the city of Zinjibar, which they have controlled since May last year, said the official, speaking on condition of anonymity. Four officers were among those killed, he said.

A medic in Aden confirmed the toll, adding that 11 others were wounded.

Some 25 other soldiers have not been accounted for, the military official said, adding that dozens of militants took part in the attack, some of whom arrived by sea.

A medic in the neighbouring town of Jaar, which is also controlled by Al-Qaeda, said 16 militants were killed in the gunfights around Zinjibar, capital of Abyan province, and their bodies were evacuated to Jaar.

The attacks came after Yemeni Al-Qaeda leader Fahd al-Quso, who was wanted in connection with the 2000 bombing of the USS Cole, was killed in an air strike in eastern Yemen on Sunday.

The October 2000 attack on the US Navy destroyer, the USS Cole, in Yemen's port of Aden killed 17 sailors and wounded 40 more.

Quso was killed when two missiles slammed near his home in Rafadh, east of Ataq, the provincial capital of Shabwa province, a tribal chief said, adding that two of the suspect's bodyguards were also killed in the raid.

Quso's name figured on an FBI list of most wanted terrorists, along with a reward of up to $5 million for information leading to his arrest.

"They attacked our positions in retaliation for the killing of Fahd al-Quso," said a military official.

He said the army had been anticipating Al-Qaeda to retaliate for the killing of Quso, saying that an alert was sent out to all units to expect an attack by the "enemy" following Sunday's air raid.

Several military officials in Sanaa told AFP on Monday that such air strikes are launched by US aircraft and coordinated by President Abdrabuh Mansur Hadi, and the army and intelligence leaderships.

In his first public speech since taking office following February elections, Hadi, who succeeded veteran leader Ali Abdullah Saleh after he stepped down following a year of protests, vowed to intensify the war against Al-Qaeda.

"The war against terrorists has not started yet, and will not be over before we purge every province and village so that the displaced can return home peacefully," Hadi warned last week.

The jihadists, who have renamed themselves the Partisans of Sharia (Islamic law) control parts of southern and eastern Yemen where the authority of Sanaa is weak.

In another part of the restive Abyan province, Al-Qaeda fighters attacked the town of Loder during the night from three different sides and clashed with army troops and gunmen from the Popular Resistance Committees, an anti-Qaeda militia.

Four armed locals were wounded, a member of the committees said on Monday.

Al-Qaeda seized Loder, 150 kilometres (96 miles) northeast of Zinjibar, in August 2010, but the army eventually drove it out.