US forces have carried out two drone strikes targeting militants in part of Afghanistan where the Taliban have clashed with purported supporters of the Islamic State group, officials said Tuesday.

The Islamic State (IS) group, also known by its Arabic acronym Daesh, has never formally acknowledged having a presence in Afghanistan but fears are growing that it is making inroads in the country.

The strikes on Monday took place in restive Achin district of Nangarhar province, on the border with Pakistan, where local media have reported battles between Taliban insurgents and IS supporters in recent weeks.

A spokeswoman for the NATO mission in Afghanistan confirmed US forces carried out two "precision strikes... against individuals threatening the force" but did not give details of who was targeted.

Provincial spokesman Ahmad Zia Abdulzai told AFP the strikes killed a total of 49 members of a "new group".

A spokesman for the National Directorate of Security (NDS), the Afghan spy agency, claimed the IS group's "number two" commander in Afghanistan was killed in an air strike in Achin, though he did not specify whether it was a drone strike.

However IS has not announced its presence or identified its commanders in Afghanistan and there was no confirmation of the NDS's claim.

Afghan officials say IS's presence in the country is so far limited to small groups and factions that have split from the Taliban. The extent of their links to the group's operations in Syria and Iraq, and the extent of the support they receive, is extremely unclear.

IS has grabbed large areas of Syria and Iraq in a brutal campaign but last month the Pentagon said the group's presence in Afghanistan was still "in the initial exploratory phase".

But the potential for IS to attract members has clearly not been lost on the Taliban, who last month warned the Middle East group's leader against waging a parallel insurgency in Afghanistan.

In February, a NATO drone strike killed Mullah Abdul Rauf Khadim, a former Taliban commander and Guantanamo detainee with suspected links to IS, in the volatile southern province of Helmand.