The man, identified as Talib Mikhlif Arsan Walman al-Dulaymi, also known as Abu Qutaybah, was captured during a Feb. 20 raid in Anah, about 160 miles northwest of Baghdad, a government announcement said.
He is Iraqi, and a Sunni, reports CBS News Correspondent Cami McCormick, and he was arrested near the Syrian border. It's believed he arranged safe houses and transportation and funneled money to Zarqawi. If true, his arrest could be key to locating the U.S. military's most wanted man in Iraq.
In other developments:
The government said the captured terror suspect "was responsible for determining who, when and how terrorist network leaders would meet with al-Zarqawi."
Al-Zarqawi, who has a $25 million bounty on his head, is believed to have orchestrated a relentless wave of car bombings, kidnappings, assassinations and beheadings across the country.
Qutaybah "filled the role of key lieutenant for the Zarqawi network, arranging safe houses and transportation as well as passing packages and funds to al-Zarqawi," the government said. "His extensive contacts and operational ability throughout western Iraq made him a critical figure in the Zarqawi network."
The government said Qutaybah was a known associate of other al-Zarqawi lieutenants already held by coalition forces, including Abu Ahmed, an al Qaeda-linked insurgent leader in the northern city of Mosul who was detained Dec. 22.
During the same Feb. 20 raid, Iraqi forces also captured another al-Zarqawi aide who "occasionally acted as his driver," the government said. The man was identified as Ahmad Khalid Marad Ismail al-Rawi, who also helped arrange meetings for al-Zarqawi.
Both suspects are Iraqi and their names belong to well-known Sunni tribes in and around the town of Ramadi, a hotbed of the insurgency in Anbar province west of Baghdad.
The government earlier announced it captured the leader of an al Qaeda-affiliated terror cell allegedly responsible for a string of beheadings in Iraq.
In a statement late Thursday, the government said Mohamed Najam Ibrahim was arrested by Iraqi National Guardsmen in Baqouba, 35 miles northeast of Baghdad. It gave no date for the arrest.
Ibrahim had carried out the beheadings with his brother, the government said.
"The two beheaded a number of citizens in addition to launching attacks against Iraqi security forces," the statement said.
The government said Ibrahim was being interrogated by authorities.
Last week, police said they arrested two other leaders of the insurgency in Baqouba, including an aide to al-Zarqawi named Haidar Abu Bawari.
Witnesses said the attack on the U.S. patrol took place around midday in Tarmiyah, 20 miles north of Baghdad.
Residents saw about a dozen injured U.S. soldiers lying on blood-splattered ground after the attack.
"I was heading to our house ... There was a group of American soldiers walking in the road while around five Humvees were parking behind them," said Waleed Nahed, 35, who lives in the area. "I heard a very loud explosion and I saw bodies flying."
He said he was about 200 yards way and believed explosives were hidden among the palm trees overlooking the street.
Nahed and Alaa Nagy, 22, who works as a guard at a nearby factory, said helicopters landed in the area 15 minutes after the explosion and took the injured soldiers away. Both said they heard gunfire after the incident.
The road was immediately blocked off by the U.S. military and Iraqi security forces.
At least 1,489 members of the U.S. military had died since the beginning of the Iraq war in March 2003, according to an Associated Press count.
Bringing Sunni Arabs, who make up about 20 percent of the population, into the government is important because they are believed to make up the core of the insurgency. They dominated Saddam Hussein's Baath party and largely boycotted the elections.
But in a move that could rile Kurds, al-Jaafari said that a dispute over the northern city of Kirkuk should be postponed until after the drafting of a new constitution. A constitution must be drafted no later than Aug. 15.