Updated

U.S. counterterrorism officials are concerned about the merger of Al Qaeda's central organization and its offshoot in Iraq, even with the death of terror leader Abu Musab al-Zarqawi, a Senate panel was told Tuesday.

"Eliminating Zarqawi is clearly a major step forward," retired Vice Adm. John Scott Redd, director of the National Counterterrorism Center, said in his testimony. "But both Al Qaeda and (Al Qaeda in Iraq) will continue on with their deadly work."

Zarqawi was killed last week in an airstrike in Iraq. He formed a loose network there that operated under several different names before he pledged allegiance to Usama bin Laden's Al Qaeda organization in October 2004. Analysts have since been studying how the two organizations — linked in name and ideology — interact.

Redd, a senior intelligence official, told the Senate Foreign Relations Committee's hearing on the changing face of terror that Al Qaeda and its core leadership remain the "pre-eminent concern" of U.S. counterterrorism officials.

But intelligence agencies also are paying close attention to other Sunni Muslim terrorist groups that are inspired by Al Qaeda, as well as homegrown terror groups, like 17 men and juveniles arrested in Canada this month.

They were allegedly plotting attacks using three tons of ammonium nitrate — three times the amount used in the 1995 Oklahoma City bombing.

"While not controlled by Al Qaeda, these new networks draw inspiration from their ideology," Redd said. "Clearly, we are not immune to that in the United States."

Redd testified alongside Henry Crumpton, the State Department's counterterrorism coordinator, and other intelligence experts.

Officials are also monitoring Hezbollah, a Shiite Muslim group with close ties to Iran, Redd said. Tensions between Tehran and Washington have grown in recent months over its nuclear program.

Redd's center — formed since the attacks of Sept. 11, 2001 — can tap into 28 different U.S. networks to allow intelligence analysts access to 5 million pieces of intelligence.

The counterterrorism hub maintains the U.S. government's master database of known or suspected terrorists. It includes over 200,000 identities, including aliases.