"Fifteen Taliban were killed, including Mullah Abdur Rahim, in Maruf district," said Afghan Foreign Ministry official Khalid Khan Achakzai.
He said the dead fighters probably came from Zabul which borders the province of Kandahar where Maruf is located.
But a former Taliban intelligence official denied the death of Rahim, who has control over southern Afghanistan where the Taliban have been most active in recent months.
Mullah Abdul Samad said: "There have been deaths on both sides but it is wrong that Abdur Rahim has been killed. It is mere propaganda."
Rahim has been suffering from wounds sustained earlier in the year in a clash with Afghan forces in Spin Boldak.
There are around 12,500 troops in the US-led force hunting Afghan resistance fighters.
Afghanistan has recently been rocked by the worst violence since the fall of the Taliban.
In recent months more than 200 people have been killed, including Taliban fighters, government soldiers and police, civilians and aid workers.