Sana'a, Yemen - Yemeni authorities were continuing the search Monday for kidnapping gang that abducted a German engineer and two of his Yemeni colleagues, local security sources said.

The sources said authorities were waiting for tips from tribal chieftains on the hideout of the kidnappers, believed to be in a rugged mountainous area in the south-eastern province of Shabwa.

Armed tribesmen kidnapped the German expert and two Yemeni engineers on Sunday afternoon as they were heading to their work site near the Arabian Sea port of Balhaf in Shabwa, some 570 kilometres south east of Sana'a.

A local source said the abductors belong to the Laqmoush tribe, and that they were demanding the release of a jailed fellow tribesman accused of murdering a man from the same tribe in 1989.

The German hostage works as a pipeline expert for Amecspie Hawk, a sub-contractor with Yemen LNG Ltd that runs the project.

Amecspie Hawk is building a 320-kilometre-long pipeline form the oil refinery in the north-central province of Mareb to the LNG exporting port of Balhaf.

Two policemen were injured in a clash with the kidnappers at a checkpoint in Azzan district, when police tried to stop the car that carried the kidnappers and their hostages on Sunday, according to a security source.

The source said one of the policemen was in critical condition and that he was rushed to a hospital in the southern port city of Aden.

Police officials said a hunt for the kidnappers was under way and that security forces had set up extra checkpoints on roads leading to the kidnappers' village in the Lamater area of Shabwa.

The kidnapping is the third involving foreigners and the second involving German nationals in about a month.

On December 15, three Germans were captured in western Yemen. They were released four days later. On January 3, a South African mother and her two sons were seized by tribesmen in the southern province of Abyan. They were released a day later.

Disgruntled tribesmen from impoverished areas of Yemen often take hostages to use as bargaining chips to press the government for aid, jobs or the release of detained fellow clansmen. (dpa)