KABUL — The US military says it has now fully withdrawn the last of the 33,000 ‘‘surge troops’’ sent to pacify Afghanistan two years ago, but it is leaving behind a landscape of rising violence and political instability that threatens to undo gains in security, particularly in former Taliban strongholds.

As the troops head home about a week ahead of schedule, the US coalition and its Afghan partners are bedeviled by a host of problems.

The tempo and audacity of Taliban attacks have increased. Insider killings of Americans by Afghan troops have raised tensions between the allies, forcing severe cutbacks in strategically vital training programs.

Both governments are arguing over whether to keep battlefield prisoners locked up without trial, while nervous officials on all sides are worrying that riots over an inflammatory anti-Muslim video, which have killed dozens in other countries, will break out here.

Friday’s milestone, which still leaves 68,000 US troops in Afghanistan, was announced by the US Defense Secretary Leon Panetta during a trip to New Zealand, while both US and Afghan officials in Kabul studiously ignored the moment, at least in public.

Some Afghans boasted that it showed their forces were ready to take over, while pro-Taliban forces exulted that they were not, but most Afghans just worried about what it would mean for the final two years of the US presence here.