Four Western aid workers, including two Canadians and a Briton, have been kidnapped in Iraq, officials say.
Abducted Briton Professor Kember was staying in west Baghdad
A senior Canadian official confirmed that two Canadian nationals were seized in the capital Baghdad on Saturday.
The UK Foreign Office later named 70-year-old Professor Norman Kember as missing and believed abducted.
It is estimated that over the past year and a half, at least 200 foreigners have been abducted in Iraq. Some have been executed by their kidnappers.
The fourth foreigner is thought to be an American, although the US embassy in Baghdad has only said that one of its citizens is missing.
In a separate incident, two Britons and an Iraqi have been killed in an attack by gunmen in Iraq after visiting holy sites.
They were travelling with a group of British Shia Muslims from London who on a pilgrimage to Iraq.
British officials say they have set up an urgent investigation into the abduction of Mr Kember, a veteran peace activist.
UK Foreign Secretary Jack Straw said officials had been in touch with Mr Kember's family and that he had discussed the matter with Iraqi Foreign Minister Hoshyar Zebari.
"We are working on the basis it is a kidnapping," Mr Straw said.
He added that the UK had a "clear and consistent" policy that it did not pay ransoms.
A multi-national hostage team is thought to be focusing on who seized the four and what their motives were.
Canadian authorities have not named their two nationals. Dan McTeague, the parliamentary secretary for Canadians abroad, repeated Canada's advisory to its citizens not to travel to Iraq.
"Under no circumstances should Canadians be there," Mr McTeague said. "The situation remains very unstable... and continues to be a danger for all foreign travellers."
In October the al-Qaeda in Iraq militant group said it had abducted two Moroccan embassy employees.
Also in October, Guardian reporter Rory Carroll was taken at gunpoint in the Baghdad suburb of Sadr City but was freed after 36 hours.
In August, US freelance reporter Steven Vincent was shot dead after being abducted in Basra, southern Iraq.