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SANAA, Jan 2 (Reuters) - Yemeni tribesmen have kidnapped a South African woman and her two sons, demanding that authorities release a group of prisoners, a local government official said on Friday.

The three tourists were seized in the province of Abyan, the official said. The prisoners whose release the abductors were demanding were relatives of the tribesmen, he added.

Last month, armed tribesmen kidnapped three Germans to press for an end to a land dispute with another tribe, and for the release of jailed fellow tribesmen. The foreigners were freed unharmed almost a week later.

Disgruntled tribesmen have often kidnapped Western tourists to demand better living conditions, schools and services in the Yemen, one of the world's poorest countries outside Africa.

Most have been released unharmed, but in 2000 a Norwegian diplomat was killed in crossfire and in 1998 four Westerners were killed during a botched army attempt to free them from Islamist militants who had seized 16 tourists. (Reporting by Mohamed Sudam)

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