WASHINGTON (CNN) -- Al Qaeda will try to tap its allies and resources in Iraq in its efforts to exact another terrorist attack on U.S. soil, according to a top government intelligence report released Tuesday.
A police officer looks for suspicious vehicles earlier this month outside Dulles International Airport in Virginia.
Officials have expressed concern in the past that the Iraq war is providing a theater for al Qaeda to train insurgents and test the terror network's capabilities.
"In addition, we assess that its association with [al Qaeda in Iraq] helps al Qaeda to energize the broader Sunni extremist community, raise resources and to recruit and indoctrinate operatives, including for homeland attacks," said the declassified summary of the National Intelligence Estimate.
But the radicalization process doesn't stop there, according to the report. Islamist Web sites, aggressive anti-American rhetoric and an increasing number of self-generating terror cells in Western countries indicate that violent factions of Islam are spreading.
Though the problem is more dire in Europe than the United States, the report said, there is evidence that extremists in the U.S. are "becoming more connected ideologically, virtually and/or in a physical sense to the global extremist movement."
Declassified portions of the completed NIE -- which represents the combined analyses of all 16 U.S. intelligence agencies -- was released Tuesday after the classified version was presented to Congress. It is the first NIE to focus on the terrorist threat to the U.S. homeland. See what previous reports said »
Mike McConnell, director of national intelligence, gave President Bush a special briefing on the report Tuesday morning, a senior administration official said. Watch McConnell discuss the new threats »
The report also warned that al Qaeda -- which it said has become "innovative in creating new capabilities and overcoming security obstacles" -- is beefing up efforts to sneak operatives into the United States.
"Although we have discovered only a handful of individuals in the United States with ties to al Qaeda senior leadership since 9/11, we judge that al Qaeda will intensify its efforts to put operatives here," stated an NIE summary.
"As a result, we judge that the United States currently is in a heightened threat environment," the summary said.
International cooperation on counterterrorism efforts has made the U.S. a more elusive target for al Qaeda -- and has also led to thwarted plots since the September 11, 2001, attacks -- but, the report warned, "this level of international cooperation may wane as 9/11 becomes a more distant memory and perceptions of the threat diverge."
Mass casualties are not the endgame for the terror network, according to the report. Al Qaeda also seeks to perpetrate a sensational attack that produces "visually dramatic destruction, significant economic aftershocks and/or fear among the U.S. population," the summary said.
The draft of the intelligence report expressed concern about the possibility of a growing number of extremists who may already be in the United States, two officials said last week. The report said al Qaeda is still in pursuit of chemical, biological and nuclear weapons.
The report also said that al Qaeda has set up a safe haven along the Pakistan-Afghanistan border from where the terror network's leaders can operate, several U.S. officials said.
The NIE analysis addresses al Qaeda's resurgence in the tribal areas of Pakistan, where President Pervez Musharraf last year gave primary responsibility for controlling the border areas between Pakistan and Afghanistan to tribal leaders.
The United States considers Musharraf an ally in the fight against al Qaeda and has been reluctant to pressure him to do more to control the border areas, where authorities believe both al Qaeda and the Taliban, vanquished from Afghanistan, have regrouped.
Musharraf repeatedly has said his government is working hard to curb terrorists and extremists in its territories.
Also included in the report:
• The Lebanon-based militant group Hezbollah, which has conducted attacks against Western interests outside the United States, may consider an attack on U.S. soil if "it perceives the United States is posing a direct threat to the group or Iran."
• Non-Muslim terrorist groups -- such as those radicalized by other religions or environmental issues -- likely will perpetrate attacks on the U.S., "but we assess this violence is likely to be on a small scale."
• Globalization and advances in technology will enable extremists to network more easily across national borders. These advances also will provide a means for extremists to "justify and intensify their anger and mobilize their resources to attack -- all without requiring a centralized terrorist organization, training camp or leader." E-mail to a friend
CNN's Kelli Arena, Pam Benson and Ed Henry contributed to this report.