WASHINGTON -- Gen. David Petraeus, commander of U.S. forces in Iraq and Afghanistan, has told his troops that despite progress on both fronts, the U.S. and its allies face a tough fight in the year ahead.

With his trademark caution, Petraeus wrote in a letter to all troops in U.S. Central Command -- stretching across the Middle East and throughout Central Asia -- that improved security conditions in Iraq remain fragile and that while the Afghan army is improving, "the difficulties in Afghanistan are considerable."

It was the first time since Petraeus took charge of Central Command on Oct. 31, following 20 months as the top U.S. commander in Baghdad, that he has offered troops what he called "my initial assessment of the situation" not only in Iraq and Afghanistan, but also in Pakistan and elsewhere in that region.

The letter, dated Dec. 9, was released by his office at Central Command headquarters in Tampa, Fla.

Petraeus has assembled a team of experts to conduct an in-depth and comprehensive review of his command area; it is expected to be completed by early February. His aides said that is separate from the "initial assessment" he offered in the letter to troops. The assessment was based on his own discussions and observations during extensive travels in the Middle East, Central Asia and elsewhere over the past few months.

"In Iraq, we are building on the progress achieved by coalition and Iraqi forces in the course of difficult operations," he wrote. He said gains have been encouraging but are still not irreversible -- a theme he and other commanders have struck many times in arguing against a rapid withdrawal of U.S. forces.

Petraeus mentioned that further troop cuts in Iraq are planned, but he was not specific.

President-elect Barack Obama has said he would consult with Petraeus and other commanders and senior civilian defense officials before carrying out his campaign promise to bring the Iraq war to an end.

"Numerous difficult issues loom on the horizon in the `Land of the Two Rivers,"' he wrote, alluding to the name derived from the important role the Tigris and Euphrates rivers have played in Iraq's history. He noted the challenges of Iraqi elections to be held in 2009, plus "resilient enemies still carrying out deadly attacks, lingering ethno-sectarian mistrust and competition" and "malign external influences."

Under a security agreement that President George W. Bush signed in Baghdad last weekend, U.S. combat forces are to be out of Iraqi urban areas by June 30 and all U.S. troops are to withdraw by the end of 2011.

"In Afghanistan, we and our Afghan partners are in a tough fight," Petraeus wrote.

Noting that developing the foundations of Afghan government and economy "is typically more construction than reconstruction," Petraeus said progress has been painstaking, with much yet to be accomplished.

"The Taliban and other elements that make up the extremist `syndicate,' aided by groups operating from sanctuaries outside Afghanistan, have significantly increased the levels of violence in Afghanistan and contested control of important areas of the country," he wrote.
The Afghan government has "yet to achieve the necessary levels of competence, integrity, capacity and legitimacy," he added.

Petraeus noted obliquely the U.S. intention to send additional combat and support troops to Afghanistan next year. More firepower, he said, will be part of a broader effort to help the Afghans as they conduct elections in 2009 and "strive to achieve progress in the security, economic and governmental arenas."

Petraeus made no explicit mention of the rising tensions between India and Pakistan as a result of the Mumbai terrorist attack in November. But he linked U.S. efforts in Afghanistan and Pakistan. He wrote that Pakistan "faces substantial difficulties of its own but has shown new awareness of the need to deal with the extremists who have not only exported violence outside Pakistan's borders but have also demonstrated the threat they pose to Pakistan's very existence."

Pakistan is in Petraeus' command area but India is not.