Istanbul  - When General David Petraeus took over as commander of US forces in Iraq 19 months ago, the country was on the brink of civil war.

More than 3,000 US soldiers had died since the invasion of March 2003 and al-Qaeda terrorists had made the western province of Anbar their regional centre of operations.

With a new strategy that included a surge of US troops, Iraqi military helpers and improved surveillance, Petraeus was able to change the picture.

But for his successor, General Raymond Odierno, who on Tuesday took charge of the 146,000 US troops in Iraq, a lot of problems remain.

This is especially the case in Diyala province, northeast of Baghdad, where many former officers and members of the secret service of ex-dictator Saddam Hussein live.

Dozens of suicide bombers, men as well as women, have blown themselves up in the province in recent weeks.

Another powder keg is the city of Kirkuk, where Kurds, Turkmens and Arabs are battling for influence as well as the proceeds from oil revenues.

According to Western analysts future success in Iraq depends in part on whether Prime Minister Nuri al-Maliki is able crack down on corruption that is rife within government ranks.

All this is well-known by Petraeus, who was rewarded for his service with a promotion as head of US Central Command, which runs military operations in the Middle East and South Asia, including Afghanistan.

In farewell remarks looking back on his tour of duty, the general was careful to avoid using the work "success" and spoke instead of "improvements."

"Your great work, sacrifice, courage, and skill have helped to reverse a downward spiral toward civil war and to wrest the initiative from the enemies of the new Iraq," he told his troops.

But he warned that the tasks facing the US-led forces in Iraq "are far from complete and hard work and tough fights lie ahead."

Even officers of Saddam's army, who counted the US troops as their worst enemies, admit that progress has been achieved.

"Under the command of David Petraeus, US forces in Iraq have made up a lot of ground, particularly in the city of Ramadi, which was an enduring cause of concern for American troops," said Ahmed al-Obaidi, a lieutenant-colonel in Saddam's elite Republican Guard.

Al-Obaidi said it was not so much the troop surge that changed the picture, but the strategy of arming and financing local Sunni forces, or Awakening Councils, to fight al-Qaeda terrorists that paid off.

"It was this strategy that cleared the way for the Iraqi army and police to operate freely in those regions that were previously under the control of armed groups," he said.

Odierno, the man who is replacing Petraeus, is on his third tour of duty in Iraq. He commanded the 4th Infantry Division in 2003 and was responsible for cracking down in an area north-west of Baghdad known as the Sunni triangle.

The capture of Saddam Hussein was also credited to his division.

But some of Odierno's critics say the ruthless raids on villages conducted by troops under the command of the shaved-headed general forced some Iraqis into the clutches of al-Qaeda, which promised revenge on the Americans.

Odierno, however, later subscribed to the more pragmatic view put forward by Petraeus that in order to win the battle for Iraq the US had to win over the trust of its people.

At the time there was speculation that a tragic incident in his private life might have contributed to this change of heart: Odierno's son, Anthony, lost his left arm in a missile attack in Baghdad in the summer of 2004. (dpa)