"As a result, the Taliban will continue to test the (Afghan forces) aggressively in 2016," it said.
The U.S. now has about 9,800 troops in Afghanistan, some of which are involved in counterterrorism missions.
In October, President Barack Obama announced that he would keep troops levels steady through most of next year. By the end of 2016, rather than draw down to a Kabul-only U.S. military presence of about 1,000 troops as previously planned, Obama decided the U.S. will maintain 5,500 troops in Kabul and Bagram. Tuesday's report said Obama's decision reflects the need to give Afghans more time to develop a credible army.
"The resilient Taliban-led insurgency remains an enduring threat to U.S., coalition, and Afghan forces, as well as to the Afghan people," the report said.
The report covers the second half of 2015, which is the first year that Afghan forces have fought without U.S. troops alongside them on the battlefield. The Afghans largely stood their ground, or managed to recover territory they temporarily conceded, but the report credited the Taliban with "improving their ability to find and exploit" Afghan vulnerabilities. The Taliban also are using the Afghan-Pakistan border as sanctuary, it said.
To illustrate the point that security conditions are still unsatisfactory, the report said the number of casualty-causing Taliban attacks from January through November rose by about 4 percent over the comparable period in 2014. The number hovered around 1,000 per month during the year before decreasing in September.
The report also said al-Qaida, which used Afghanistan as a base from which to launch the Sept. 11, 2001 terrorist attacks, has a "sustained presence" in eastern and northeastern Afghanistan and remains a threat to the United States. It did not estimate how many al-Qaida fighters are in the country.
Other problems that have persisted in Afghanistan since the U.S.-led invasion in October 2001 are still unsolved, the report said. Revenue from opium trafficking, for example, continues to sustain the insurgency and Afghan criminal networks. The report cited an increase in extortion and kidnappings by low-level criminal networks.
Despite years of U.S. efforts to build an effective Afghan army and police, security is still threatened by a host of insurgent and extremist networks. The report said these include the Taliban, the Haqqani Network, and to a lesser extent al-Qaida as well as an Islamic State affiliate that is openly fighting with the Taliban for establishment of a safe haven.
__
Associated Press reporters Deb Riechmann in Washington and Lynn O'Donnell in Kabul contributed to this report.