NATO's US-led mission in Afghanistan is withholding key information about Taliban attacks, a US government watchdog said Friday, potentially making insights into the war harder just as the Pentagon slashes its troop presence.

The Resolute Support (RS) mission previously disclosed data on "enemy-initiated attacks", one of the few remaining public metrics of the conflict and the strength of the Taliban and other insurgent groups. In its quarterly report released Friday, the office of the Special Inspector General for Afghanistan Reconstruction (SIGAR) said RS had stopped providing numbers.

Instead, RS gave only a short statement noting the Taliban stepped up attacks in March, immediately after the signing of a US-Taliban deal that was supposed to pave the way to peace talks. "Between March 1 and 31, the Taliban refrained from attacks against coalition forces; however they increased attacks against (Afghan forces) to levels above seasonal norms," RS said, according to the report.

Under the deal, US and other foreign forces will quit Afghanistan by July 2021 if the Taliban start peace talks with Kabul and stick to various security commitments. In the week ahead of the February 29 deal signing in Doha, violence plummeted during a partial truce and US officials hoped attacks would stay low.

Instead, the Taliban immediately resumed assaults on Afghan forces. During the deal negotiations, the Taliban had agreed to stop hitting foreign troops, but there was no such prohibition on targeting Afghan forces.

RS told SIGAR that it chose to restrict data because enemy attacks were now a "critical part" of discussions "regarding ongoing political negotiations between the US and the Taliban". SIGAR noted the Pentagon said it might release the information in the future.

The move to withhold attack numbers follows a trend of diminishing insights into America's longest war, which the US has given up ever winning and is instead trying to end through a political agreement that will provide face-saving cover to leave Afghanistan.

In 2018, RS stopped providing data on how much of the country the Taliban held or contested, amid criticism the war was mired in an intractable stalemate. That followed a decision by the Afghan government to classify data on how many of its soldiers and police were getting killed by the Taliban, after shocking figures showed several thousand were dying each year.

Data on enemy attacks "was one of the last remaining metrics SIGAR was able to use to report publicly on the security situation in Afghanistan," the watchdog said. The Pentagon is on course to cut its troop numbers from about 12,000 to 8,600 in the coming months.