Taliban fighters, whom US-led forces spent billions of dollars trying to defeat, are now openly active in 70% of Afghanistan.
Months of research across the country shows that the Taliban now control or threaten much more territory than when foreign combat troops left in 2014.
The Afghan government played down the report, saying it controls most areas. But recent attacks claimed by Taliban and Islamic State group militants have killed scores in Kabul and elsewhere.
Afghan officials and US President Donald Trump have responded by ruling out any talks with the Taliban. Last year Mr Trump announced the US military would stay in the country indefinitely.
IS is more active in Afghanistan than ever before, although it remains far less powerful than the Taliban.
The Taliban are now in full control of 14 districts (that’s 4% of the country) and have an active and open physical presence in a further 263 (66%), significantly higher than previous estimates of Taliban strength.
About 15 million people – half the population – are living in areas that are either controlled by the Taliban or where the Taliban are openly present and regularly mount attacks.