Washington ? Osama bin Laden’s al-Qaida network has stepped up its financial activity markedly in recent weeks, suggesting some leaders are reasserting control and may be seeking to finance more attacks against American interests, a U.S. official says.

The increased flow of money corresponds with a recent increase in communications between surviving al-Qaida members, the official said, speaking only on condition of anonymity.

At a checkpost on the southern edge of Gardez, Afghanistan, soldiers loyal to warlord Bacha Khan Zardran, stand guard. Zardran is working with the U.S. Special Forces to flush out al-Qaida and Taliban from the mountains of eastern Afghanistan. A report Saturday indicated that financial transactions by the al-Qaida had increased recently, perhaps signaling a regrouping of the Osama bin Laden-led terrorist effort.

The communications, detected by U.S. intelligence, have occurred between small groups of al-Qaida fighters and some Taliban allies, officials said. Much of the activity is centered in northwestern Pakistan near the Afghan border although some money and communications are going elsewhere, one official said.

The activity suggests some known al-Qaida leaders are re-establishing control over surviving elements of the terrorist network, the official said, declining to name the leaders. U.S. intelligence has detected a significant boost in money transfers within al-Qaida to people who could use it to prepare attacks on American interests, although the official offered no specifics on potential attacks.

“There’s lots of signs al-Qaida is reconstituting itself,” said Vince Cannistraro, a former CIA counterterrorist chief. “Internet traffic has picked up enormously. Money is moving around. There is some evidence leadership is active.”

The fate of many of al-Qaida’s top commanders is unknown. While several have been killed in the Afghan war, and a few captured, many are believed to have hidden in caves in Afghanistan to wait out the U.S. bombing campaign.

Bin Laden has been silent for months. U.S. intelligence has had vague hints he remained in the Afghan-Pakistan border region. Officials have few doubts he is still alive.

President Bush last week called bin Laden “marginalized,” and intelligence officials, during classified briefings to congressional leaders, suggested he had been wounded and may be quietly recovering somewhere. But they acknowledge there is no hard evidence on his condition.

Cannistraro said finding bin Laden remains as important as ever.

“It’s pretty clear they don’t know where he is, which is why they are de-emphasizing the importance of him,” he said.

Other senior leaders capable of masterminding attacks, such as Ayman al-Zawahri and Abu Zubaydah, remain at large. Al-Zawahri, bin Laden’s doctor and spiritual adviser, survived bombing in Afghanistan that killed his family. Zubaydah, previously based in Pakistan, had contacts with al-Qaida cells around the world.

The U.S. official said that while there is some evidence of al-Qaida’s leadership at work, many of its cells are capable of conducting attacks independent of top commanders.

The hijackers who conducted Sept. 11 attacks received money from bin Laden’s financial chief, also known as Mustafa Ahmed al-Hisawi and Shaikh Saiid. On Sept. 13, he fled the United Arab Emirates for Pakistan, and his whereabouts are unknown.

The global financial crackdown on terrorist money has hindered al-Qaida’s ability to finance attacks, officials said. But it never stopped.

On Friday, a top Treasury Department official said more than 150 countries have joined the United States in helping to freeze accounts and block transactions between suspected terrorists including al-Qaida.

Overall, the United States has frozen more than $35 million, while the combined effort of other countries has halted about $70 million, said Mike Romey, special assistant to the treasury secretary for national security, who was speaking to students in Kentucky.

Al-Qaida’s money is believed to come from a number of sources bin Laden’s personal fortune, donations of seemingly legitimate Islamic humanitarian concerns, and honey and gold trading.