Taliban fighters, whom US-led forces spent billions of dollars trying to defeat, are now openly active in 70% of Afghanistan.
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.
“When I leave home, I’m uncertain whether I will come back alive,” said one man, Sardar, in Shindand, a western district that suffers weekly attacks. “Explosions, terror and the Taliban are part of our daily life.”
The extent to which the Taliban have pushed beyond their traditional southern stronghold into eastern, western and northern parts of the country is clearly visible.
Areas that have fallen to the Taliban since 2014 include places in Helmand province like Sangin, Musa Qala and Nad-e Ali, which foreign forces fought and died to bring under government control after US-led troops had driven the Taliban from power in 2001. More than 450 British troops died in Helmand between 2001 and 2014.
In the areas defined as having an active and open Taliban presence, the militants conduct frequent attacks against Afghan government positions. These range from large organised group strikes on military bases to sporadic single attacks and ambushes against military convoys and police checkpoints.
122 districts (just over 30% of the country) did not have an open Taliban presence. These areas are ranked as under government control, but that does not mean they were free of violence.
Kabul and other major cities, for example, suffered major attacks – launched from adjacent areas, or by sleeper cells – during the research period, as well as before and after.
Violence has soared since international combat troops left Afghanistan three years ago.
More than 8,500 civilians were killed or injured in the first three-quarters of 2017, according to the UN. Final figures for the year are awaited. The vast majority of Afghans die in insurgent violence but civilians often suffer as the military, with US backing, fights back, both on the ground and from the air.
Although much of the violence goes unreported, big attacks in the cities tend to make the headlines. Such attacks are occurring with greater frequency and the Afghan security forces appear unable to stop them.
During the research period, gunmen stormed the headquarters of Kabul’s Shamshad TV, leaving one staff member dead and 20 wounded. IS said it carried out the attack. There were other attacks in Kandahar, Herat and Jalalabad.
In the last 10 days of January three attacks left the capital reeling, with more than 130 people dead. Last May, Kabul experienced the deadliest single militant attack since 2001. At least 150 people were killed and more than 300 injured when a massive truck bomb was detonated in what was supposed to be the safest part of the city. No group has said it carried out the attack.
The rising toll of violence has left the capital’s residents feeling increasingly vulnerable.