Efforts are continuing to find the five Britons snatched by armed men in Baghdad on Tuesday.
Iraqi police commandos are now patrolling the finance ministry
Foreign Secretary Margaret Beckett said the situation remained "quite unclear", but insisted everything possible was being done to secure their release.
It is not yet known who carried out the kidnap, but a senior aide of radical Shia cleric Moqtada Sadr said his group - the Mehdi Army - was not involved.
The five were seized at the finance ministry in the Sadr City suburb.
On Wednesday, US and Iraqi troops carried out raids and sealed off parts of the city close to where the kidnapping took place.
The US military said a number of militants had been arrested but would not confirm whether the raids were linked to the missing Britons.
There has been speculation that the group were abducted in retaliation for the killing of a Mehdi Army militia leader. The Foreign Office has said there is no firm indication as to who was responsible.
Speaking at the G8 summit in Berlin, Mrs Beckett said families of the missing were being kept informed of any progress.
And she said everything possible was being done "to find out where they may be and why they're being held".
Meanwhile, Iraq's national security adviser Muwaffak al-Rubaie pledged to bring the kidnappers to justice.
"This group of kidnappers, they are terrorists, whether they are Shia extremists or Sunni extremists," he said.
The five men - a computer expert and four bodyguards - were taken from the finance ministry building in Palestine Street.
The kidnappers, dressed in police uniforms, walked past ministry guards and staged the capture without firing a shot, senior Iraqi officials said.
A police source told the BBC dozens of police vehicles were used in the operation.
The four kidnapped security guards were working for Canadian-owned security firm Gardaworld.
The company is one of the biggest suppliers of private security in Iraq, and is mainly staffed by Britons.
The kidnapped computer expert was employed by Bearingpoint, a US management consultancy which has worked on development projects in Iraq since 2003.
Private contractors are known to be unpopular with Iraqis.
About 200 foreigners of many different nationalities have been kidnapped in Iraq over the past four years, though the number has fallen dramatically since a few years ago.
This is thought to be the first time Westerners have been abducted from a government facility.