A group of influential Sunni clerics called Wednesday for the release of five Westerners taken hostage last week in a wave of kidnappings, saying they should be granted their freedom as a humanitarian gesture.

The Association of Muslim Scholars, believed to have contacts with some Sunni insurgent groups, has helped mediate the release of other Western captives in Iraq.

The five include four aid workers from the group Christian Peacemaker Teams — Tom Fox, 54, of Clearbrook, Va.; Norman Kember, 74, of London; and James Loney, 41, and Harmeet Singh Sooden, 32, both of Canada — and German archaeologist Susanne Osthoff, 43.

The association said releasing Osthoff would recognize Germany's "positive" stand toward Iraq. Germany strongly opposed the U.S.-led invasion in 2003.

In her first speech to parliament, German Chancellor Angela Merkel vowed that her government will "not let ourselves be blackmailed" by militants who kidnapped Osthoff and her driver.

"The government is doing everything in its power to bring the German citizen and her driver as soon as possible to safety," Merkel said.

The statement also noted that Osthoff is married to an Iraqi Muslim, "who is a member of the Shammar tribe from Mosul and she works as an archaeologist." The Shammar tribe is one of the largest in Iraq and includes Shiites as well as Sunni clans. Vice President Ghazi al-Yawer is a senior figure in the tribe.

Osthoff and her Iraqi driver were seized Friday, and later were shown in a videotape blindfolded on a floor, with armed militants standing beside them.

Kidnappers threatened to kill them unless Germany halted all contacts with the Iraqi government.

Stephan Kroll, an archaeologist at Munich's Ludwig-Maximilian University where she had studied, said Osthoff had admitted she was worried "something could happen to her."

On visits in recent years to her old colleagues to ask for donations, Osthoff said she was "stopped and held" on several occasions by unidentified groups seeking money, Kroll said in a telephone interview. "She said she always got away because she could speak Arabic and because she told them she was on a humanitarian mission," he said.

Kroll said Osthoff had left the institute in 1991 without completing her master's course and had "very limited expertise" as an archaeologist. He said he doubted reports that antiquities smugglers could have kidnapped her because she was disturbing their work.

University staff and friends of Osthoff had pleaded with her not to go back to Iraq.

"She never listened. She went her own way," Kroll said. "She thought it was her mission to help the people."

The Association of Muslim Scholars said the release of the Christian aid workers would recognize their "good efforts in helping those in need."

In Ramallah, in the West Bank, Mufti Ikrema Sabri, the Palestinians' top Muslim clergyman, also called for their release.

"These aid workers have stood beside (the) Palestinian people and it's our duty now to stand beside them," he said.

Palestinians in several towns said they had worked with the activists and asked Sabri to issue the appeal.

The four were taken captive Saturday and appeared in a video broadcast by Al-Jazeera. A previously unknown group calling itself the Swords of Righteousness Brigade claimed they were spies working under the cover of Christian peace activists.

The Christian group, which has had activists in Iraq since October 2002, dismissed the accusation they were spies.

"They are four men who came to Iraq to work for peace and to explain their opposition to the occupation. They are not spies," Doug Pritchard, a Canadian co-director for Christian Peacemaker Teams, told CBC-TV. "All of the Iraqi organizations and individuals who know us know that too, and we've encouraged them to speak out and they are doing that."

Fox worked at youth summer camps and was staunchly opposed to war, said Anne Bacon, clerk of a Quaker meeting in Clear Brook, Va. He kept in touch through e-mails and a Web journal.

"He feels very strongly that the occupation in Iraq is a mistake," the family said in a statement.

Kember was a professor of medical physics at St. Bartholomew's Hospital until retiring 13 years ago, and he was a longtime pacifist.

Loney is a longtime peace activist and was arrested in 1991 outside the ruling Conservative party headquarters in Toronto for protesting Canada's involvement in the Gulf war.

Sooden, an electrical engineer, had been studying literature at the University of Auckland in New Zealand before traveling to Iraq. He previously studied at McGill University in Montreal.

The last American to be kidnapped was Jeffrey Ake, a contract worker from LaPorte, Ind., who was abducted April 11. He was seen in a video aired days afterward, held with a gun to his head, but there has been no word on his fate since.