Members of Ansar al-Islam, the extremist Muslim group pushed from its northern Iraq enclave by U.S. and Kurdish forces a week ago, have begun surrendering at the Iranian border where hundreds of fighters sought refuge.

At least a dozen fighters surrendered today to Kurdish officials, and negotiations were underway to receive at least 150 more, said an official of the Patriotic Union of Kurdistan (PUK), which controls the eastern half of the Kurdish autonomous zone and whose militia joined with U.S. Special Forces to rout the group.

"The numbers are fluctuating," said the official, who asked not to be named. "A bunch crossed the border themselves."

The Bush administration claims that Ansar al-Islam has ties to al Qaeda and set up training camps for terrorists. Most Ansar members are Kurds, but some Arabs joined last year after losing refuge in Afghanistan, accounting for the group's links to al Qaeda, according to U.S. officials.

A PUK delegation has traveled to Tehran, the Iranian capital, to demand the return of scores of Arabs who had fought alongside Ansar's fighters. "We want them to deliver the Arab Afghans back to us," said the PUK official.

The corner of northern Iraq that Ansar held until last week hugged the mountains that form the border between Iraq and Iran, and Iran was widely believed to be supplying ammunition and logistical support to the group. Ansar opposed the mainstream secular Kurdish groups that have governed northern Iraq since 1991, establishing an autonomy that analysts said Iran considered a dangerous temptation to its own Kurdish population.

When U.S. Special Forces led 6,000 Kurdish militiamen against Ansar positions on March 28, Ansar fighters fled to Iran, which detained at least the Kurdish members of Ansar. They began trickling back over the weekend, inquiring whether a previous offer of amnesty remained open, the PUK official said.

But the whereabouts of the Arab fighters is not clear. Last year Iran returned to their home countries several dozen al Qaeda members who had crossed into Iran from Afghanistan after the U.S. attack on that country. Diplomats and other sources noted, however, that several senior al Qaeda figures continued to find refuge in Iran.

How many Ansar fighters remain alive is not known. U.S. Special Forces commanders told reporters after the battle that of about 700 Ansar fighters, more were killed than escaped. But because many died in caves or on remote ridges, a casualty count was not available. Kurdish sources said 22 of their militiamen died, about half the figure announced earlier.

A Special Forces commander also said U.S. intelligence officers had collected documents and other evidence that appeared to indicate poisons or chemical weapons were being manufactured at an Ansar compound in the village of Sargat. Secretary of State Colin L. Powell singled out the compound in a February presentation to the U.N. Security Council that also claimed Ansar had links to President Saddam Hussein's government.

The U.S. commander said the evidence collected from the heavily bombed compound at Sargat had been shipped to the United States for testing.