Some consider his pledge over the weekend to be an effort to elevate his status and improve his resources and fund raising. Others view it as an attempt to broaden his audience and improve recruitment.
While U.S. authorities try to sort out just how close al-Zarqawi is to bin Laden, many agree that al-Zarqawi's motives are worrisome.
"It is certainly not a positive development, but in terms of what it means in practical terms, it isn't clear at this point," said a U.S. counterterrorism official, speaking on condition of anonymity.
Al-Zarqawi and his movement, now named Tawhid and Jihad (search ), are believed to be behind dozens of attacks and much resistance to Iraqi and U.S.-led forces in Iraq. That includes a series of beheadings.
The counterterrorism official said al-Zarqawi's statement, posted on a Web site known for carrying militant Islamic content, is viewed as credible. It came at the start of Ramadan, although some U.S. officials have tried to play down any connection to the holy month of fasting and prayer.
A defense official, also speaking anonymously, said the military is trying to determine why al-Zarqawi made the statement now, as the U.S. military steps up attacks against the insurgency in Iraq, and what the statement means.
In recent days, U.S. air strikes have targeted safe houses used by the al-Zarqawi network in Fallujah, the central Iraq city believed to serve as the group's base. U.S. officials have said the attacks are believed to have killed major leaders of al-Zarqawi's organization.
The defense official said al-Zarqawi may be trying to appeal to a larger audience and adopt bin Laden's broad objective to attack the United States. But "we are not in his head," the official added.
A Palestinian born in Jordan, al-Zarqawi has been a known terror operative for some time. He was a shadowy figure until he made a name for himself as the most dangerous terror plotter in Iraq.
Al-Zarqawi's previous goal had been to overthrow the government of Jordan, his home country, U.S. officials believe. After the 2003 U.S.-led invasion of Iraq, he has focused his efforts there.
The United States is offering $25 million for information leading to al-Zarqawi's death or capture.
By so brazenly challenging the United States, al-Zarqawi has made himself a hero to Islamic militants in Iraq and elsewhere.
"Politically he is riding high, although his organization may be getting pounded," said Daniel Byman, a senior fellow at the Saban Center at the Brookings Institution.
The pledge of support to bin Laden "enables him to tap into resources that were previously not available," Byman said. "It could be that he is strong enough politically, but on a day-to-day basis he may need more money and people."
A debate about al-Zarqawi's relationship to bin Laden has waged for years inside the U.S. government. Assorted authorities have considered him a rival of Al Qaeda, an ally of bin Laden or a true deputy inside the organization. He is believed once to have run a training camp in Afghanistan.
White House spokesman Trent Duffy said Sunday the administration always has seen ties between al-Zarqawi and Al Qaeda, "which underscores once again why Iraq is the central front in the war on terror."
Both terror leaders could benefit, the counterterror official noted. For al-Zarqawi, the statement has propaganda value by elevating him in the eyes of his followers, the official said. Al Qaeda also gains because it is in the group's interest to be aligned with the leading Islamic militant in Iraq.
Al-Zarqawi's Internet declaration said he and bin Laden communicated eight months ago, and "viewpoints were exchanged" before the dialogue was interrupted. "God soon blessed us with a resumption in communication, and the dignified brothers in Al Qaeda understood the strategy of Tawhid and Jihad," the statement said.
It's unclear to U.S. authorities whether the statement is akin to the merger between Egyptian Islamic Jihad and Al Qaeda in 1998. Today, Islamic Jihad's leader, Ayman al-Zawahri, is bin Laden's top deputy. The two are thought to be hiding somewhere along the Afghan-Pakistani border.
Yet it has taken some time for al-Zarqawi to align himself officially with Al Qaeda. The counterterrorism official said it is possible the terror leaders had difficulty communicating securely. Government officials say bin Laden and al-Zarqawi also may have had differences over tactics and strategy.
Arabic-language wiretaps played last month at the German trial of four of the suspected Sept. 11, 2001, plotters revealed some of the divisions.
When al-Zarqawi's operatives in Germany told him in 2001 that they were also raising money for Al Qaeda, he became angry.
"If something should come from their side, simply do not accept it. Just forget it!" al-Zarqawi said. His voice was identified in court by a jailed follower, although the authenticity has been questioned.