Updated

American forces have detained 19 alleged members of Usama bin Laden’s terrorist network in Iraq, according to civilian administrator L. Paul Bremer (search).

Authorities determined that the captives were tied to Al Qaeda (search) through interrogations and documents the suspects were carrying, Bremer said in a Pentagon news conference. The administrator added that there are currently 248 non-Iraqi fighters being held by Americans in Iraq.

Bremer said he did not know what countries the Al Qaeda suspects came from, but he did say the largest number of foreign fighters — 123 of the 248 – hailed from Syria. He said most of them were entering Iraq via "ratlines" from that country.

The next-highest numbers came from Iran and Yemen, he said. He did not have precise figures for those countries.

The terrorists streaming into Iraq represent the biggest threat to rebuilding the country, Bremer said. Likewise, turning Iraq into a democracy is key to making progress in the war on terror, he said.

"We don't want Iraq to become a breeding ground for terrorism in the future," Bremer said.

Bremer also stressed that, thus far, reconstruction efforts have not been thwarted by fighting between U.S. forces and their enemies.

Bremer was in Washington, D.C., this week to testify before Congress in support of President Bush's $87 billion request for spending on Iraq. About $20 billion of that request would pay for reconstruction projects overseen by Bremer's Coalition Provisional Authority (search), the civilian administration in Iraq.

Bremer and other Bush administration officials have repeatedly accused Syria of being an obstacle in the Iraq conflict, first by allowing shipments of military goods to Saddam Hussein before and during the war and now by allowing terrorists to cross the same border.

Syrian officials deny interfering with U.S. efforts in Iraq.

Some terrorists are members of Ansar al-Islam (search), a militant group linked to Al Qaeda whose base in northern Iraq was wiped out by coalition forces early in the war, Bremer indicated.

Ansar has regrouped and re-entered Iraq with perhaps several hundred members, he said.

"They're a very dangerous group," he said.

The Associated Press contributed to this report.