Sana'a, Yemen  - The governor of Yemen's south-eastern province of Shabwa has vowed to pursue tribesmen who abducted a German oil expert and two Yemeni engineers, the official Saba news agency reported on Wednesday.

"Security apparatuses are determined to pursue all those involved in the crime of kidnapping the German engineer and to arrest them at the earliest," the agency quoted the governor, Ali Hassan al-Ahmadi, as saying during a meeting with the freed hostage.

The kidnappers, who belong to the Laqmoush tribe, released the German expert and his Yemeni companions on Tuesday, two days after they abducted them in Shabwa, some 5700 kilometres south east of the capital Sana'a.

Saba said the governor also "expressed regret" to the German ex- hostage for the "criminal kidnap act that he subjected to by a group of outlaws."

The freed hostage, who works as a gas pipeline expert for Amecspie Hawk, returned to his work site on Wednesday, a company source told Deutsche Presse-Agentur dpa.

Amecspie Hawk is a subcontractor with Yemen LNG Ltd, which runs a giant gas exporting project in the south-eastern Yemeni port of Balhaf.

The source, who spoke on condition of anonymity, said the ex- hostage had to fly later in the day to Sana'a to meet German embassy officials.

Embassy officials were not available for comment.

Armed tribesmen kidnapped the German expert and two Yemeni colleagues on Sunday as they were heading to their worksite. The abductors were demanding the release of a jailed fellow tribesman accused of murdering a man from the same tribe in 1989.

A security source the kidnappers agreed to set the hostages free after a breakthrough was reached in negotiations with the government following the intervention of Yemeni President Ali Abdallah Saleh's half-brother and military commander Ali Mouhssien al-Ahmar.

Al-Ahmar made pledges to the abductors to discuss their demand in exchange for releasing the hostages, the source said.

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

Three Germans were captured in western Yemen on December 15, and 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 one 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)