Investigators continue to uncover several pieces of the secretive network that finances Usama bin Laden's worldwide terrorism operation.

In the last two months, U.S. officials have exposed financial bloodlines from honey and diamond dealers to U.S. money-wiring outfits sending millions to Somalia.

But they concede they have a long way to go to fully disrupt the network.

"I think it is not possible to know yet how many more of these kinds of organizations may exist and what other inventive mechanisms may exist that we haven't discovered yet," Treasury Secretary Paul O'Neill said.

President Bush announced Wednesday the United States was targeting two organizations funneling large amounts of cash to bin Laden's Al Qaeda network: Al Taqua and Al-Barakaat.

Known as hawalas, the two groups operate largely underground in more than 40 countries, including the United States, and move funds to Al Qaeda through companies and nonprofits they run, the administration said.

Investigators believe tens of millions of dollars a year flow overseas through Al-Barakaat. Much of that was sent by Somali residents of the United States to relatives, with the networks skimming money off for Al Qaeda through exchange fees.

Investigators believe it works like this: Networks charge a fee to relay money, with one-fourth of the fee kept by the hawala broker who took the money in the United States and another quarter going to the receiving hawala dealer, in Somalia, for instance. The remainder, or half the fee, would be sent to the main company. That's the point where Treasury officials believe money gets funneled to Al Qaeda.

In Somalia, where the Al-Barakaat group is based, President Abdiqasim Salad Hassan said Thursday that his fledging government will set up a special committee to investigate the suspected terrorist links.

A criminal complaint filed in Boston suggested some of the money leaving the United States went first to the United Arab Emirates. The money was wired in small increments below $10,000 to escape notice by banking regulators, officials said.

The operation was the first for Treasury's new Green Quest terrorist tracking unit.

That's not the only creative money-moving mechanism terrorism investigators have discovered.

Treasury last month identified three honey-related businesses in Yemen believed to be fronts secretly moving money for Al Qaeda. The U.S. government previously linked the owner of one to the main Al Qaeda base in Europe used to move money, weapons and the network's members.

Foreign officials also believe Al Qaeda may be using the illegal African diamond trade to make and hide money. And some U.S. experts think bin Laden has profited from Afghanistan's opium trade.

Some believe the battle against terrorist financing may never end.

"I don't think you're ever going to know if you've destroyed it completely. It's not a physical target in the way a base is or a military target is," said Mark Lowenthal, an intelligence consultant and former staff director of the House Intelligence Committee.

"You have a twofold program: One, you have to continually track the money sources, and two, once you know about them you have to disrupt them. Once you find one, you have to know there's another one."

This week, 62 entities and people were added to a list of suspected terrorist associates targeted by the United States. The United Arab Emirates and Britain ordered financial institutions to freeze their assets, officials announced Thursday.

The earlier list included 88 groups or people whose assets were being targeted because of their ties to Al Qaeda and other terrorist groups.

To date, 112 countries have issued blocking orders. The United States has frozen $26 million in assets of Afghanistan's ruling Taliban and Al Qaeda since Sept. 11; another $17 million was blocked by other countries, bringing the global total to $43 million, a Treasury spokeswoman said.

In coordinated raids Wednesday, Customs agents seized evidence and shut down Al-Barakaat companies in four cities: Boston, Minneapolis, Seattle and Columbus, Ohio. The Treasury Department froze assets of nine organizations and two people in the United States, most with links to Al-Barakaat.

In addition, FBI agents raided two Fairfax County businesses seeking evidence of terrorist transactions. The companies cater to the Somali community in northern Virginia, not far from the Treasury Department office where Bush announced the crackdown.

In Boston, Mohamed M. Hussein and Liban M. Hussein were charged with running an illegal money-transmitting business, according to a criminal complaint. Officials said Mohamed Hussein was in custody.

Liban Hussein was located with family members at a townhouse in Ottawa by the Toronto Star and told the paper he was innocent. "I have nothing to hide, to be honest with you. If they (the police) need me, I'm here, or I'll even go to them," Hussein said.

A lack of full international cooperation is the biggest challenge the United States faces as it tries to further undermine terrorist financing, said Jack Blum, former special counsel to the Senate Foreign Relations Committee.

"What we really need is a system that operates relatively seamlessly where all of the countries cooperate in the course of an investigation," Blum said. "And of course it doesn't work that way. It's all tangled up in questions of sovereignty."

Sen. Carl Levin, a sponsor of anti-money laundering legislation recently passed by Congress, said the United States must pressure other countries to adopt tougher laws. Levin's legislation requires banks to take greater steps to make sure accounts have no connection to terrorists or other criminals. Still, he said, investigators' pursuit of terrorist money will have to be relentless.

"We've tried to close those cracks, but they'll try to find other cracks and create more cracks," said Levin, D-Mich.

The Associated Press contributed to this report.