Unidentified gunmen opened fire on CNN reporter Brent Sadler and his television crew as they ran a checkpoint on their way out of the city north of Baghdad, and the CNN armed guard in the car returned fire in a dramatic exchange on live worldwide television.

"That's gunfire. We just come under attack! Under attack! We're OK, we're OK. We're under fire. That confirms our worst fears. We've just run a checkpoint. We have come under automatic machine gun fire. They tried to stop us," Sadler said as sounds of shooting were heard.

The convoy then came under fire a second time from a vehicle pursuing them on a highway as they fled the city.

The back window of one of the vehicles in their convoy was shot out.

"One of our vehicles has taken some shots. That was a pretty ugly moment," Sadler said after the second attack from the chasing vehicle.

The shoot-outs indicated that at least part of the city of 200,000 people appeared still to be in control of Saddam's regime. But he and his crew had earlier driven part of the way into Tikrit without difficulty.

Earlier the team travelled through an abandoned ammunition depot and Republican Guard barracks on the outskirts without incident. They then entered the city after a resident told them coalition forces were negotiating the surrender of the city.

The resident, identified as a teacher, said Saddam was "finished" in the city, a traditional stronghold the regime.

Any last stand from Saddam's regime is expected to come in Tikrit, which has been the traditional power base of Saddam and his Baath party. At least part of a Republican Guard division had been believed to be in or around the city.

"Where are the final divisions of the Republican Guard?" Sadler said earlier as he drove in unopposed.

The fall of the city would all but mark the end of the war to topple Saddam launched on March 20, which has seen every other major city in the country of 26 million people fall into the hands of the US-led coalition.

Earlier footage showed an abandoned military base on the outskirts of the city as Sadler drove to Tikrit from the city of Mosul.

Many buildings along the way had been bombed-out, after days of air strikes from US and British forces. Armoured personnel carriers were parked around the buildings.

US commanders said Saturday a large number of marines were heading north of Baghdad toward the city.

"Tikrit is one of the areas where we still have concerns that there may be presence of regime forces and we have been relentless in our efforts focused at the Tikrit area," Brigadier General Vincent Brooks said at the war command's headquarters in Qatar.

Another military spokesman, Captain Frank Thorp said a significant number of US marines left Baghdad and were heading north.

"We have been using air power on the military forces for more than a week. Only time will tell when we get into Tikrit or any of the other areas," said Thorp.

SPACE.WIRE