The ministry had received no information about the four Christian activists by late morning Saturday, a spokesman said. He asked that his name not be used due to the sensitivity of the situation.
The previously unknown Swords of Righteousness Brigade set Saturday as a deadline for killing Norman Kember, 74, of London, Tom Fox, 54, of Clear Brook, Virginia, and Canadians James Loney, 41, and Harmeet Singh Sooden, 32.
The group seized the four members of the Christian Peacemaker Teams two weeks ago. It first set a Thursday deadline but then extended it until Saturday, without setting a precise hour.
On Friday, Sunni Arab clerics used their main weekly religious service to plead for the hostages' lives because of their humanitarian work and condemnation of the U.S.-led war in Iraq.
"We ask those who have authority and power to do their best to release the four European people who work in Christian peace organization," cleric Ahmed Hassan Taha told worshippers in Baghdad's Sunni stronghold Azamiyah. "In fact those activists were the first who condemned the war on Iraq."
Residents gathered outside the mosque held aloft banners demanding their release.
"The people of Azamiyah will not forget the honest positions of the peacemakers," read one. Another said "we demand the release of the abducted peacemakers."
In other developments:
The Canadian Islamic Congress to Iraq also sent an envoy, Ehab Lotayef, to try to win the activists' release.
"We hope that they would be released as soon as possible because Christmas is approaching and I hope that they will be with their families by then. We hope that this regrettable story will have a happy end," Lotayef said.
Lotayef told reporters that Loney had worked among Palestinians and "was forbidden by Israelis to enter Palestine again."
A French aid worker and a German citizen are also being held by kidnappers. There was no word early Saturday on the fate of an American hostage, Ronald Allen Schulz, after an Internet statement in the name of the Islamic Army in Iraq claimed to have killed him.
Iraqi officials believe the revival of foreigner kidnappings may be part of a bid to undermine Dec. 15 elections, in which Iraqis will choose a parliament to serve for four years.
U.S. officials hope a big turnout among the Sunni Arab minority, the foundation of the insurgency, will help quell the violence so that American and other foreign troops can begin to go home next year.
In a statement Friday, U.S. Ambassador Zalmay Khalilzad called on Iraq's political parties to condemn all attempts at voter intimidation.
"The Iraqis deserve an election that is free from intimidation and violence," he said in a statement. "Iraqi citizens will stand up to those who would intimidate them and vote for those who can bring them a better future."
Elsewhere, American troops detained a high-ranking member of al Qaeda in Iraq after he was turned in Friday by residents of Ramadi, the U.S. military said.
Amir Khalaf Fanus, also known as "the Butcher," was wanted for murder and kidnapping, Marine Capt. Jeffrey S. Pool said in a statement. The military said another 1,200 Iraqi Security Force soldiers were recently stationed in Ramadi. They included 1,100 Iraqi special police commandos and a mechanized Iraqi army company of about 100.
Al Qaeda in Iraq, led by Jordanian terror boss Abu Musab al-Zarqawi, has threatened to disrupt the balloting.
Sunni Arabs largely boycotted the previous election in January, enabling rival Shiites and Kurds to win most of the 275 seats. This time, most Sunni clerics and leaders are urging fellow Sunnis to vote.
"The date of Dec.15 is landmark event, Sunni cleric Ali al-Zand told a congregation in Baghdad's Umm al-Qura mosque. "It is a decisive battle that will determine our future. If you give your vote to the wrong people, then the (U.S.) occupation will continue and the country would be lost. Participation in the elections is a must and it is a religious duty."