Taliban leader Mullah Omar Wednesday hailed as "legitimate" peace talks aimed at ending Afghanistan's 13-year war, in his first comments on the nascent dialogue, easing concerns that it lacked the leadership's backing.

Afghan officials sat down with Taliban cadres last week in Murree, a tourist town in the hills north of Islamabad, Pakistan, for their first face-to-face talks aimed at ending the bloody insurgency.

They agreed to meet again in the coming weeks, drawing international praise, but many militant commanders openly questioned the legitimacy of the Taliban negotiators, exposing dangerous faultlines within the movement.

But in his annual message before Eid-ul-Fitr, the festival marking the end of the fasting month of Ramadan, the reclusive leader backed negotiations -- though he did not refer specifically to last week's meeting.

"If we look into our religious regulations, we can find that meetings and even peaceful interactions with the enemies is not prohibited," he said in a statement on the Taliban's website.

"Concurrently with armed jihad, political endeavours and peaceful pathways for achieving these sacred goals is a legitimate Islamic principle."

Several informal meetings have been held in recent months between Taliban representatives and Afghan officials and activists, but last week's meeting is seen as a significant step forward.

Afghan officials have not said when and where the next round of negotiations will take place, but it is widely expected to be conducted after Eid.

- Fears of IS emergence -

Wednesday's statement marks the first comments on the process from Mullah Omar, about whom rumours of ill-health and even death regularly emerge.

In the absence of a clear lead from the top, some fighters have fallen back on the Taliban's traditional position, that there can be no meaningful talks until all foreign forces leave Afghan soil.

NATO ended its combat mission in Afghanistan at the end of December, but a smaller residual force remains in the country to train Afghan forces, due to leave altogether by the end of 2016.

But Wednesday's statement is "different from previous Taliban statements", said Kabul-based political analyst Ahmad Saeedi.

"In addition to war, the Taliban leader talks about peace and negotiations," Saeedi told AFP.

"There is no doubt a gradual change is developing in the Taliban's attitude. It is now for the Afghan government to use this golden opportunity and engage them smartly."

But talks are dependent on another contributing factor -- the emergence of a local branch of the Islamic State, the Middle Eastern jihadist outfit that last year declared a "caliphate" across large areas of Iraq and Syria that it controls.

The Taliban warned IS last month against expanding in the region, but this has not stopped some fighters, inspired by the group's success, defecting to swear allegiance to IS chief Abu Bakr al-Baghdadi instead of the invisible Mullah Omar.

US drone strikes over the past week have killed dozens of suspected IS-linked cadres in Afghanistan, including the group's Afghanistan-Pakistan regional chief Hafiz Saeed.

The notoriously uncompromising IS has shown no desire to negotiate -- and if the Taliban faultlines widen, there is a danger the talks process could drive more of its hardline fighters into the arms of the Middle Eastern jihadist group.

"We have... directed all our mujahideen to preserve their unity and forcefully prevent all those elements who attempt to create differences, damage this jihadi front," Omar's statement said in an oblique reference to IS.