Fighting is raging around three major cities in southern and western Afghanistan as Taliban militants seek to seize them from government forces.
Taliban fighters have entered parts of Herat, Lashkar Gah and Kandahar.
They have made rapid gains in rural areas since it was announced almost all foreign troops would go by September.
But the fate of these key cities could be crucial amid fears of a humanitarian crisis and how long government forces will be able to hold out.
The fundamentalist Islamist militia is already thought to have captured up to half of all Afghanistan's territory, including lucrative border crossings with Iran and Pakistan.
In Lashkar Gah, capital of the southern province of Helmand, a local source said insurgents were only a few hundred metres from the governor's office on Saturday.
They had also come close to it on Friday, but the commander of Afghan forces said they had inflicted significant casualties on the militants, who were forced to retreat overnight.
Having already captured large amounts of rural territory, and a number of border crossings, the Taliban's firm focus is now on Afghanistan's cities. The situation is fluid but Lashkar Gah, capital of Helmand Province where many US and British soldiers lost their lives, looks the most vulnerable right now. Pro-Taliban social media accounts have uploaded videos of their fighters in the heart of the city.
Afghan special forces are being sent in to help push them back, but one local resident told us even if that does end up happening, the Taliban's advance is a powerful assertion of their strength.
The militants are understood to have taken up some positions in the homes of ordinary families, which will make it harder to dislodge them. More lengthy and bloody fighting looks to be ahead.