The New York Times quoted Jordanian security officials as saying that the former head of al-Qaeda in Iraq had recruited about 300 fighters who were trained in Iraq and sent back to their home countries to await further orders.
The move signalled an attempt by al-Zarqawi, who was killed in a US air strike last Wednesday, to strengthen his movement and turn it into a global terror organisation to challenge Osama bin Laden, the paper said.
Jordanian officials described al-Zarqawi, himself a Jordanian national, as a leader with strong organisational capabilities who changed his routine whenever one of his followers was detained.
Jordanian intelligence officials had followed al-Zarqawi for decades, but efforts to find him intensified after a series of deadly hotel bombings in the Jordanian capital, Amman, in November in which dozens of people, mostly Jordanians, were killed.
Jordanian officials told the newspaper that a new intelligence unit, called Knights of God, was formed after the attacks and that its agents were dispatched to Iraq and neighbouring countries.
The agents found al-Zarqawi about two months ago and were able to confirm US intelligence on his whereabouts on the day he was killed, they added.
US counterterror officials told the newspaper that they had also tracked a flow of fighters into Iraq from Arab countries such as Saudi Arabia and Egypt.
However, they said they believed the number of fighters to be significantly lower than the number given by the Jordanians.