BAGHDAD, Iraq (CNN) -- U.S. forces moved by daylight into the heart of Baghdad on Saturday, demonstrating coalition troops' ability to strike the Iraqi capital "at the time and place of their choosing," according to the U.S. Central Command.

In a briefing at Central Command headquarters in Qatar, Air Force Maj. Gen. Vincent Renuart said two task forces of the U.S Army's 3rd Infantry Division conducted an operation from south of the Iraqi capital north to the Tigris River and then west toward Baghdad's airport, which is under coalition control.

"It was, I think, a clear statement of the ability of the coalition forces to move into Baghdad at the time and place of their choosing," Renuart said.

While just outside the capital, CNN correspondent Walter Rodgers, who is embedded with the lead element of the 3rd Infantry Division -- the 3rd Squadron, 7th Cavalry -- described the incursion as a reconnaissance mission.

"It does appear very clearly from the maps we've seen that what the army is striving to do at this point is carve out chunks of the city," Rodgers said. "Bite off a chunk of Baghdad and then take that chunk and literally dismember the city zone by zone so that each of these zones falls under the control of the U.S. Army."

Sources in Baghdad told CNN's Nic Robertson that they'd spotted U.S. troops in several parts of the city and that gunfire and sirens were heard.

Sources also spoke of seeing Iraqi forces, including tanks, gathered mostly on the western part of Baghdad. Those sources described those Iraqi troops as including Republican Guard and Fedayeen Saddam fighters and forming a "front-line position."