BAGHDAD, Iraq (CNN) -- A man believed to be al Qaeda's No. 2 operative in Iraq has been killed, a U.S. Defense Department official confirmed to CNN.

The military official said Abu Azzam, a "significant" figure in the al Qaeda network in Iraq, held senior positions in the al Qaeda in Iraq network in Baghdad and Falluja and had a personal relationship with the most-wanted militant Abu Musab al-Zarqawi.

"This creates a void for al Qaeda in Iraq, in their leadership, for a while," a U.S. military spokesman said.

The spokesman said Azzam was slain at 4:50 a.m. Sunday in a residential high-rise in Baghdad during a coalition-Iraqi operation.