Fighting between police and separatist fighters erupted after security forces put up checkpoints [EPA]

Four policemen and two gunmen were killed overnight in the south of Yemen during a clash at a checkpoint set up by security forces.

Separately, a tribal chief and two of his bodyguards were killed in an ambush that government officials blamed on al-Qaeda.

Violence broke out late on Saturday after security forces put up a checkpoint outside Habilayn, in Lahej province, where they then reportedly clashed with members of the separatist Southern Movement.

Local officials and medics initially said at least two policemen and one fighter were killed, and two other fighters shot and wounded in the clashes.

But a Southern Movement official, speaking anonymously to the AFP news agency, said that two of the movement's fighters had been wounded by shrapnel and later died in a hospital.

Local officials also revised their tally on Sunday, reporting four policemen dead.

The Southern Movement official said the fighters had died when the Yemeni army fired on a position held by the group on a mountain overlooking Habilayn.

South Yemen, where many residents complain of discrimination by the federal government in Sanaa in the allocation of resources, was independent from 1967 until 1990, when it united with the north.

It launched an unsuccessful secession attempt four years later. Formed in 2009, the Southern Movement is a mix of secessionists and those who seek greater autonomy for the region.

Mediator targeted

In Abyan, another southern province, a leader from the Al Fadl tribe who had reportedly been leading mediation efforts with some al-Qaeda fighters was killed in an ambush along with two bodyguards.

Sheikh Hussein Saleh Mashdal was killed overnight, a Yemeni security official told AFP.

Mashdal had been "leading the mediation between the authorities and alleged Qaeda militants" in the city of Loder, one of Mashdal's relatives told AFP.

Yemeni security forces have been battling Houthi rebels in the north, Southern Movement fighters in the south and members of Al-Qaeda in the Arabian Peninsula (AQAP) for more than a year.

On Saturday, Yemen arrested 14 suspected al-Qaeda fighters in Abyan.

Amnesty International, a London-based human rights group, issued a report in August condemning the Yemeni government for carrying out targeted killings and arrests without affording suspects due process.