Six aid workers were kidnapped by armed tribesmen near the Yemeni capital Sana'a on Tuesday, official media and local tribal sources said, dpa reported.
The state-run SABA news agency said the six were a German, a Colombian, an Iraqi, a Palestinian and two Yemenites.
A local source told dpa that they worked for the United Nations Office for the Coordination of Humanitarian Affairs (OCHA).
The gunmen intercepted the vehicles carrying the workers as they were leaving an area near the capital. Government sources said they were taken to a location around three kilometres away from the main road leading into Sana'a.
The kidnappers are demanding the release of a man detained in the capital's central prison in exchange for freeing the workers. Negotiations are underway with the tribesmen, SABA reported.
Meanwhile, gunmen opened fire at Information Minister Ali al-Amrani's car as he left a cabinet meeting in the capital. He escaped unhurt, witnesses said.
In the southern Abyan province, 11 militants affiliated with al-Qaeda were killed in three drone strikes, residents said. Three local al-Qaeda leaders were among those killed.
In September, al-Qaeda's spiritual leader in Yemen, Anwar al-Awlaki, was killed by a US unmanned aircraft.
Insurgents have taken advantage of a year of political turmoil in Yemen to expand their influence in the impoverished Arabian Peninsula country.
Outgoing President Ali Abdullah Saleh used the threat of militants to seek support from the West and extend his stay in power, despite months of protest against him.
After 33 years in power, Saleh signed a Gulf Cooperation Council-brokered deal in November to step down.
Presidential elections are scheduled for February 21. The parliament unanimously nominated Vice President Abd Rabbu Mansur Hadi as the sole presidential candidate for the polls.