Four Iranian pilgrims and a German woman were missing in Iraq on Tuesday after being seized by gunmen, in an apparent return to the dire security conditions foreigners faced from hostage takers in the country last year.
The abductions follow the seizure of four foreign aid workers - two Canadians, a Briton and an American - who were snatched from their vehicle in western Baghdad on Saturday.
The six Iranians, four men and two women, were taken on Monday with an Iraqi woman as they were returning from a visit to a Shia holy site, Iraqi police said.
The three women were later released, but it was not clear under what circumstances.
Tehran has asked Iraqi Prime Minister Ibrahim Jaafari's government to assist in securing the release of the remaining four hostages, Iranian television reported.
The group was abducted as they made a pilgrimage to a Shia shrine in the city of Balad, a mixed Shia and Sunni Arab town about 80 km (50 miles) north of the capital Baghdad.
Gunmen had opened fire on a bus carrying the pilgrims, seriously wounding the driver, police said. The driver, Hameed Hashim, told Reuters he was beaten by around six gunmen before they made off with the hostages, one of whom was his mother.
Those abductions followed the kidnapping of Susanne Osthoff, a German archaeologist missing since Friday.
In a videotape broadcast on Tuesday, unidentified kidnappers threatened to kill Osthoff unless Berlin stopped co-operating with Iraq's US-backed government, Germany's ARD TV reported.
Germany's government said it had set up a crisis unit and was working to secure her release. ARD said the videotape of the threat to kill Osthoff, said to be a fluent Arabic speaker who has lived in Iraq for years, was handed out in Baghdad.
Extracts from the tape showed three armed, masked figures surrounding two people sitting on the ground with their eyes covered. One of the masked figures appeared to be reading from a piece of paper.
There had been a lull in the kidnapping of Westerners in Iraq, with the most recent case before this week being the abduction of Irish journalist Rory Carroll in Baghdad in October. Carroll was released unharmed after 36 hours.
US, British and Canadian authorities are also trying to track down their missing nationals, who were working for peace and humanitarian group Christian Peacemaker Teams (CPT), one of the few remaining aid groups operating in Iraq. Britain's Foreign Office has identified one of the four as Briton Norman Kember, 74.