Armed men killed four members of the political party of Yemen's ousted president Ali Abdullah Saleh in an ambush outside Sanaa on Friday night, the party said.
General People's Congress officials were travelling on the road to Maareb province when attacked, the party's website said. Eight were wounded.
It was not clear if the group was targeted because of its party affiliation and a tribal source in al-Jawf where some of the men worked said it could have been a tribal vendetta.
Saleh was forced to step down as president in February after a year-long uprising. Restoring stability in Yemen has become an international priority for fear that Islamist militants will further entrench themselves in a country neighbouring top oil exporter Saudi Arabia and lying on major world shipping lanes.
Saleh was succeeded by his deputy Abd-Rabbu Mansour Hadi, who has U.S. backing for a transition process that aims to balance the interests of groups including a Shi'ite Islamist movement in north Yemen, southern secessionists and tribal and Sunni Islamist groups which benefitted under Saleh's rule.
Saleh, who ruled for 33 years, remains head of the GPC which retains half the seats in a transitional cabinet.