Recent setbacks include brief fall of Kunduz to the Taliban, struggle in Helmand province and raid on airport in Kandahar

By Phil Stewart

WASHINGTON, Dec 15 (Reuters) - Afghanistan's overall security deteriorated in the second half of this year, with Taliban militants staging more attacks and inflicting far more casualties on Afghan forces, the Pentagon said in a grim report to the U.S. Congress released on Tuesday.

The Pentagon's assessment, offering statistics and details on attack trends, was yet more evidence of Afghanistan's struggle to blunt a resilient Taliban insurgency despite 14 years of U.S. military engagement.

Recent setbacks include the brief fall of the northern city of Kunduz to the Taliban, a months-long struggle in Helmand province and an insurgent raid on the airport in the southern city of Kandahar last week that killed 50 civilians, police and security personnel.

In perhaps its most stark disclosure, the semiannual Pentagon report said casualties among Afghan national defense and security forces, or ANDSF, rose 27 percent from Jan. 1 to Nov. 15, compared with the same period last year.

That figure, counting personnel killed and wounded, came a year after a top U.S. general said Afghan casualties were already unsustainable.

Although the Pentagon praised Afghan forces for regaining territory and becoming increasingly capable of staging large-scale operations, it assessed their overall performance as "uneven and mixed."

The Taliban offensives in Helmand and Kunduz showed that the Afghan government forces "remain reactive," the report said.

"This allows the Taliban to foster the impression that the ANDSF cannot control key population centers," it said.

The report cited recent surveys showing that public confidence among Afghans in the country's security forces remained high, at 70 percent, but was down from 78 percent in March.

The Pentagon acknowledged steps by Afghan President Ashraf Ghani's government to address leadership challenges within the military, including moves to replace ineffective officers.

EXPLOITING VULNERABILITIES

The Taliban has also increased the number of effective attacks it has been able to wage by about 4 percent in the first 11 months of 2015 compared to the same period of last year. The number of effective attacks peaked at more than 1,000 in June and July.

"Insurgents are improving in their ability to find and exploit (Afghan forces') vulnerabilities, making the security situation still fragile in key areas and at risk of deterioration in other places," it said.

The report acknowledged a threat from Islamic State forces in Afghanistan, far from the Islamist militant group's stronghold in Iraq and Syria. Islamic State has seized pockets of terrain from the Taliban in Nangarhar province, it said.

In September, Islamic State attacked a U.N. vehicle and, in a single day, struck 10 Afghan security force checkpoints in Nangarhar province, it noted.

"The group continues to recruit disaffected Taliban and formerly Taliban-aligned fighters, most notably the Islamic Movement of Uzbekistan," the report stated.

Apart from the Taliban and Islamic State, the report said al Qaeda sought to reconstitute its ability to strike the West. It also noted an October operation to destroy an al Qaeda training camp in Kandahar, the existence of which alarmed some analysts.

President Barack Obama reversed his policy on Afghanistan in mid-October, saying he would prolong the U.S. military engagement by maintaining a force of 9,800 through most of 2016.

Obama had previously aimed to withdraw all but a small force based at the U.S. embassy in the capital, Kabul, before he leaves office in January 2017. Under the new plan, troops will be drawn down to 5,500 starting sometime in 2017.

American troops have fought in Afghanistan since a U.S. invasion in 2001 that toppled the Taliban government that harbored the al Qaeda network responsible for the Sept. 11 attacks that year on the United States that killed about 3,000 people.

More than 2,300 U.S. troops have died in the Afghan war effort since the 2001 invasion, although American military deaths have fallen in recent years. The report said there were 12 U.S. military deaths from June to November.

(Reporting by Phil Stewart; Editing by Will Dunham)

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