Foreign Ministry officials paid a tearful tribute Monday to two colleagues who were assassinated Saturday in an ambush in northern Iraq.

At a memorial service, Foreign Minister Yoriko Kawaguchi praised Katsuhiko Oku and Masamori Inoue for their "frontline" efforts in trying to determine how Japan can help reconstruct the nation.

"If Japan (is) able to play a role in rebuilding Iraq, it (will be) because Mr. Oku and Mr. Inoue did their best to find out the (nation's) needs and talked with the people of Iraq," Kawaguchi told about 500 ministry employees.

"Mr. Oku and Mr. Inoue were the motor and driver (of Japan's reconstruction efforts in Iraq)," she said.

Kawaguchi called on ministry officials to act as one and take over the pair's efforts.

Some ministry officials wore black ties; some cried.

"We lost colleagues with courage and a sense of mission," according to Vice Foreign Minister Yukio Takeuchi.

"Never was so much (in the field of human conflict) owed by so many to so few," Takeuchi said of his two fallen colleagues' mission, quoting a famous remark by the late British Prime Minister Winston Churchill.

U.S. President George W. Bush sent a letter of condolence Monday morning to Prime Minister Junichiro Koizumi and expressed his gratitude for Japan's assistance on Iraq.

In the letter, Bush "expressed his sympathy" for relatives of the two victims, Koizumi told reporters.