KABUL, Afghanistan - Afghanistan's president warned his people on Tuesday that the coming year will be difficult as U.S.-led forces slowly start handing over responsibility for the country's security to Afghan forces.

Hamid Karzai also renewed a call for the closure of foreign bases that run reconstruction and development programs, and the private security companies that protect many construction projects funded by international donors.

The Afghan president has repeatedly criticized the so-called provincial reconstruction teams, or PRTs, for undermining the central government by offering alternative sources of funding and public works. And he has likened the heavily-armed security companies to private militias.

Karzai said people should expect a "very important and sensitive year, a year when we will face crisis, a year when we will face difficulties because of the changes in our country."

Speaking at an event marking International Women's Day, Karzai said some of the difficulties included the attempt to start peace talks with the Taliban, Afghanistan's future relationship with the United States and the transition from coalition troops to Afghan forces.

The Afghan government has pledged to take over security gradually and on a province by province basis, starting this year, with the goal of overseeing the entire country by 2014. Karzai plans to announce the first provinces that will shift to Afghan oversight on March 21 -- the first day of spring and the beginning of the Afghan calendar year.

"This transition process will be followed gradually and will be completed in the next three to four years, all the security and administration affairs are going to be transferred to the Afghan side," Karzai said.

The first handover is expected to take place in districts and provinces where there has been little fighting and where the growing Afghan army and police have enough manpower and capacity to take control. The U.S. is also expected to announce the withdrawal of some of its troops in July.

Although the international coalition has made gains against the insurgency following a surge of 30,000 U.S. troops last year, U.S. military officials are expecting an increase of fighting in the spring -- when fighters return to the battlefield after the poppy harvest and a winter break.

Insurgents are expected to try and regain battlefield losses in the south and increase attacks in the north and east, along the porous border with Pakistan's lawless tribal areas where insurgents and al Qaeda affiliated groups have safe havens. The Taliban are also expected to increase the number of suicide attacks and attempts to assassinate against government officials.

Karzai said shutting down PRT's and private security companies will be a major part of the transition process.

"In some ways PRT's are helpful, but they are parallel structures with the Afghan government, so it is good to get rid of them," he said.

The PRTs are joint military-civilian organizations that are designed to help Kabul provide services, such as digging wells and fixing roads, outside of the capital where the central government's reach is limited. They rely on foreign assistance because funds often don't trickle down from the national government. There are now more than two dozen PRTs scattered around the country, many in areas where the military is applying its counterinsurgency operations.

NATO plans to eventually transition the bases, but closing them prematurely could make it more difficult for aid donors to bypass the central government's top-heavy bureaucracy in Kabul, where deep-seated corruption remains a significant problem despite Karzai's repeated pledges to tackle graft.