KABUL — In a rare public airing of recurring differences between U.S. military officials and a U.S. watchdog agency on Afghanistan, the agency reported this week that it had been provided with inaccurate figures about the declining number of Afghan security forces, leading it to publish an excessively negative report on the problem.

The Special Inspector General for Afghanistan Reconstruction, known as SIGAR, said in a quarterly report to Congress last month that there had been an 11 percent drop in the number of Afghan soldiers and police over the past year. The alarming finding cast doubts on progress being made by Afghan and U.S. officials to expand and strengthen the wartime forces.

But this week, SIGAR issued a second report saying the drop was much less severe, blaming “erroneous” information provided by U.S. military officials in Afghanistan. It said that the officials had informed SIGAR of the error and that the corrected numbers still showed a “sharp decline” in force strength, “but not as sharp of a decline” as previously reported.

Press officers at the U.S.-led NATO mission here, known as Resolute Support, said Wednesday they were “caught by surprise” when the first SIGAR report came out, triggering dramatic headlines about the steep drop in forces. Then they discovered an error in military calculations that had left about 17,000 troops unaccounted for and reported their new finding to SIGAR.

Lt. Col. Martin O’Donnell, the mission’s chief press official, said the missing 17,000 troops, whose border units had been transferred from the national police to the army, accounted for about half the total decline. He said that when the error was discovered, the correct figures were sent to SIGAR.

But SIGAR officials, in a sharply worded news release, said the faulty information was “the latest in a series of problems” the agency has faced with responses from the Defense Department to its requests for information about Afghan forces. 

The agency also complained that since the middle of 2017, officials at the U.S.-led NATO mission in Afghanistan “have classified or marked not releasable to the public large amounts of data in a seemingly haphazard fashion.” It said the agency has no way to independently verify statistics provided by U.S. military officials.

SIGAR said the incorrectly reported force total was 296,409 and the corrected total was 313,728. Aside from the 17,000 transferred border troops, it said the military did not say “what other factors” contributed to the mistaken report. 

Inspector General John F. Sopko and his office have clashed with U.S. military officials in the past, mostly over their refusals to reveal information that they consider too sensitive. In 2015, SIGAR complained that so much data was being kept classified that the agency was unable to publicly report on “most of the U.S. taxpayer-funded efforts to build, train, equip and sustain” Afghan forces.

This week, in the newly revised report, Sopko requested that Congress and the secretary of defense “remind all DOD components of their statutory duty to provide accurate and timely data” on Afghan forces for SIGAR’s reports.