By Missy Ryan
KABUL (Reuters) - Defense Secretary Robert Gates met Afghan President Hamid Karzai on Monday at a time of increased strain between Kabul and its Western backers and with important security transition milestones looming.
Karzai complained ahead of Gates's unannounced visit after nine Afghan children were mistakenly killed by helicopters from the NATO-led International Security Assistance Force (ISAF).
Karzai will soon unveil a timetable for the start of a handover of security responsibility from foreign forces to Afghans. The process is to begin in July and be complete by 2014. Officials said it would be the focus of Gates's trip.
Gates is expected to visit parts of southern and eastern Afghanistan where NATO commanders say they have weakened the Taliban and created "bubbles" of security they hope to link up.
But civilian casualties have clouded the relationship and diverted attention from transition plans, with blunt exchanges between Karzai and U.S. leaders after a string of recent accidental killings, mainly in remote eastern provinces.
Analysts said making strong statements over civilian casualties allowed Karzai to rally public support, but would have little long-term effect because his relations with Washington were already so badly strained.
"That being said, there is legitimate and growing anger within Afghanistan over ISAF-caused deaths," said Joshua Foust, a fellow at the American Security Project.
Karzai has said a rare and candid apology by ISAF commander General David Petraeus was "not enough". The boys were killed while collecting firewood in a volatile eastern province.
President Barack Obama has also expressed his "deep regret", but Karzai told a meeting of advisers on Sunday, which Petraeus attended, that civilian casualties caused by foreign troops were "no longer acceptable".
Karzai described such casualties as the main cause of strained relations.
Gates visited a military hospital at the vast Bagram base north of Kabul soon after arriving and reiterated Washington's long-term commitment to Afghanistan.
"You've had a tough winter and it's going to be a tougher spring and summer, but you've made a lot of headway and I think you've proven with your Afghan partners that this thing is going to work," he told troops at the base.
"DEATH TO AMERICA"
Major General John Campbell, commander of NATO-led forces in eastern Afghanistan, said 90 percent of civilian casualties in his area were caused by insurgents. Of the rest, most came during "escalation of force" incidents such as when a car failed to slow down as instructed at a checkpoint, he told reporters.
Hundreds of Afghans chanting "Death to America" gathered in the capital on Sunday in protest. There have been at least four similar incidents, mainly in the east, in the past three weeks.
International concern over civilian casualties has also grown and the fallout from the recent incidents threatens to hamper peace and reconciliation efforts, with a gradual drawdown of the 150,000 foreign troops to begin in July.
U.S. and NATO leaders have agreed to Karzai's ambitious timeline for foreign combat troops to leave by 2014. Karzai will announce on March 21 where and when the district-by-district, province-by-province transition will begin.
NATO and Afghan forces are working on identifying areas to be put under Afghan control, even if foreign forces stay nearby.
Campbell said the number of attacks in his theater had risen 21 percent over the past year but that their effectiveness -- in terms of casualties or damage -- had fallen by 28 percent.
But he said progress was being made on security and governance. "Some days it's two steps forward and one step back, but it's progress," Campbell said.
Violence last year hit its worst levels since the Taliban were ousted in 2001, and bloodshed has spread out of Taliban strongholds in the south and east into the north and west. (Writing by Paul Tait; Editing by Paul Tait and Ron Popeski)