The United States is hoping a strategy similar to the one it used to improve security in Iraq, including an influx of troops, will work in Afghanistan -- one of president-elect Barack Obama''s priorities.

But US and Afghan officials say the mission will be more difficult here as Afghanistan is splintered by tribal rivalries and weakened by the existence of militant safe havens across the border in Pakistan.

"We cannot just take the tactics, techniques and procedures that worked in Iraq and employ them in Afghanistan," General David Petraeus, commander of US forces in the Middle East and Central Asia, recently told Foreign Affairs.

At the start of 2006, Afghanistan was touted as a US military success, while Iraq was mired in a seemingly endless spiral of violence.

Today, the tables have turned: 2008 was the deadliest year for US soldiers in Afghanistan since they arrived in 2001, and the least deadly in Iraq since the start of the invasion there in 2003.

Washington helped reduce the violence in Iraq and pave the way for progress toward political reconciliation by sending more troops, intensifying operations and co-opting some of the rebels into militias paid to help maintain security.

The US military is hoping to implement a similar plan in Afghanistan, where security has worsened in the past two years as the Taliban-led insurgency has gathered pace.