WASHINGTON - Attacks on Afghan security forces increased nearly threefold last year as U.S. officials struggled to find enough military staff to train them, according to a report that details the challenge President Barack Obama faces to stabilize the troubled nation.

Obama recently announced a plan to send 17,000 additional U.S. troops to Afghanistan and is weighing a request by ground commanders to send even more. Meanwhile, the president is conducting a sweeping strategy review intended to define the U.S. mission.

In a report Monday, the Government Accountability Office said attacks on local forces in Afghanistan increased from 97 to 289 between October 2007 and October 2008. The national police force were most often targeted, losing an average of 56 officers each month in 2007 and 2008.

The GAO noted, however, that U.S. and Afghan officials have made gains in the country, including overhauling the structure of the police. More U.S. personnel would be needed to bolster existing programs that have already proved successful, the report stated.

For example, the Defense Department determined that about three-quarters of the police units trained through a particular program were capable of at least partially conducting operational missions with help. While such results are deemed promising in a poor country struggling to build up independent security forces, officials estimate that 1,500 more U.S. troops are needed to expand the program. Previously, officials had been able to redirect staff assigned to train Afghan army units, but demand for U.S. trainers has spiked as officials try to boost the Afghan army from 80,000 to 134,000 individuals.

A separate U.S.-led program helped to trim a too-large officer corps in the Afghan National Police and boost pay for the rank and file.

Japan will pay six months' salary for Afghanistan's 80,000 police officers, an effort to curb violence so aid workers can attend to humanitarian needs, two senior Japanese envoys said Monday after meeting with the U.S. representative for Afghanistan and Pakistan.

The US$124 million will be handed over by the end of March for distribution by a United Nations Development Program fund. They said the money is part of a $300 million Japanese package that also will pay for children's vaccines and new clinics, teachers and schools. Japan has pledged $2 billion in aid for Afghanistan, of which nearly $1.5 billion has been handed out.