Gunmen opened fire on veteran CNN reporter Brent Sadler and his crew after they refused to stop at the checkpoint leaving the city north of Baghdad.

An armed guard in the car returned fire in a dramatic exchange on live worldwide television, and one of the drivers in the convoy suffered a light head wound from flying glass.

"That's gunfire. We've just come under attack! Under Fire! 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.

Sadler's team was then fired on a second time from a vehicle chasing them on a highway. The back window of one of the vehicles was shot out.

"One of our vehicles has taken some shots. That was a pretty ugly moment," Sadler said after coming under pistol fire in the second attack.

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.

Sadler and his crew earlier drove part of the way into Tikrit without difficulty, passing abandoned armoured vehicles, ammunition depot and Republican Guard barracks.

They entered the city after a local resident, identified as a teacher, told them that militias loyal to Saddam had fled and coalition forces were negotiating the surrender of the city. He said Saddam was "finished" there.

"There are unconfirmed reports that there are attempts by coalition forces to negotiate a peaceful surrender of Tikrit," Sadler said as his convoy moved out of danger.

"But Tikrit, Saddam's heartland, we can confirm is still in the hands of Saddam Hussein's loyalists, armed loyalists and Baath Party officials, and we have just had to shoot our way out of that location," he said.

In Washington, a Pentagon official reacted to the firing on the CNN crew with a warning for journalists against being reckless

"There are still pockets of resistance around Tikrit. We are very cautious about it. It's a clear sign that Iraq is still dangerous place," said the official, who requested they not be named.

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

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.

As the CNN team drove toward Tikrit from the captured city of Mosul, it broadcast footage of burned out buildings 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