The United States is investigating whether men arrested in England with traces of the biological weapon ricin are linked to an Islamic extremist group in northern Iraq that has experimented with the poison, officials said Thursday.

A senior Bush administration official said U.S. intelligence has indications of connections between the group of Algerians arrested in the United Kingdom and Ansar al-Islam, a Kurdish group which U.S. counterterrorism officials have said has ties to Al Qaeda. The official, speaking on condition of anonymity, would not elaborate.

Several U.S. counterterrorism officials said they have not established any definitive link and they have no evidence that connects either to the government of Iraqi President Saddam Hussein.

Officials are investigating whether a substance that may be useful in making chemical or biological weapons was transferred from Ansar al-Islam, through the country of Georgia, to the Algerian network in England, officials said. They declined to identify the substance, but said it was not ricin or the nerve agent VX, as some reports have suggested.

Last year, Ansar al-Islam experimented with ricin and other potential biological weapons, but U.S. officials do not believe the efforts were very sophisticated. The group's leader was recently detained in Europe.

The officials, speaking on the condition of anonymity, said the British ricin suspects are linked to the roundup of suspected extremists in France that started in December.

Since Jan. 5, British authorities have arrested several Algerians on suspicion of terrorism in raids. At one of their apartments, police discovered traces of ricin, which is derived from the widely cultivated castor bean plant. The poison can kill within days and there is no antidote or treatment.

The Algerians' aims have not been made clear.

The Bush administration says fears of Saddam delivering chemical or biological weapons to terrorists is a main reason for threatening war against Iraq. Some in the U.S. government have suggested a connection between Ansar al-Islam and Saddam's government, but many counterterrorism officials dispute that.

Ansar al-Islam is in Kurdish territory in northern Iraq, largely beyond Saddam's reach. The group, numbering a few hundred fighters, is believed to be loosely affiliated with Al Qaeda, having sent about a dozen followers to Afghan camps before Sept. 11, 2001.

Saddam, too, has studied ricin as a weapon, although his primary biological weapon is thought to be anthrax, according to U.S. intelligence officials.

As Arab members of Al Qaeda have been fleeing overland from Afghanistan through Iraq, some have been given shelter by Ansar al-Islam members. U.S. officials say an Al Qaeda leader, Abu Musab Zarqawi, is believed to have gone through Baghdad for medical treatment after Sept. 11, but it is unknown whether he did so with the sanction of Saddam's government.