Kidnapped German relief worker Heinrich Struebig turned 50 Sunday, his second birthday in captivity.

Struebig is among the 13 Westerners, including six Americans, missing in Lebanon and believed held mainly by pro-Iranian Shiite Muslim factions.No group has claimed to hold Struebig, who was abducted with fellow German relief worker Thomas Kemptner, 29, in the southern city of Sidon on May 16, 1989. The two worked for the German ASME-Humanitas aid agency.

The kidnapping of the Germans was linked to the case of Shiite terrorist Mohammed Ali Hamadi, who is serving a life sentence in Germany for involvement in the 1985 hijack of a TWA jetliner to Beirut.

Hamadi was arrested in Germany in January 1987. He was sentenced to life imprisonment on May 17, 1989, one day after Struebig and Kemptner were kidnapped.

German news reports had claimed Struebig was kidnapped by the Hamadi family in an attempt to get a mild sentence for Hamadi.

One of Hamadi's brothers, Abdul Hadi Hamadi, is the Beirut security chief for the pro-Iranian Hezbollah, or Party of God, which is believed to be the umbrella for hostage-holding factions.

American Terry Anderson, chief Middle East correspondent for The Associated Press, is the longest-held foreign captive. He was kidnapped on March 16, 1985 in Beirut.