Seven Germans, a Briton and a Korean have been kidnapped in the Saada area of north Yemen.
A government source said one of the Germans worked in a local hospital, which the others were visiting.
It comes as Yemen announced it has arrested a man described as the lead financer of al Qaeda in Yemen and Saudi Arabia.
A security source said Hassan Hussein Alwan, a Saudi national, was seized two days ago in Marib province in the east of Yemen.
Militant activity in Yemen, a revolt in the north and a secessionist movement in the south has unsettled Western governments and Saudi Arabia.
On Friday, tribesmen in Saada released 24 doctors and nurses they had abducted a day earlier with a demand that authorities should free two prisoners.
The 24, most of whom were Yemenis but also included Egyptians, Indians and Filipinos, were working at a Saudi-backed hospital in the Saada area.
In 2004, tribesmen in Saada led by members of the Houthi clan began an intermittent rebellion against the government in protest at what they said was economic and religious discrimination.