Mohammad Yaqoob Mujahid said in a speech to members of Afghanistan's security forces, broadcast by state television on Saturday, that fighting outside Afghanistan is not religiously sanctioned "jihad" but rather war, which had been barred by Supreme Leader Hibatullah Akhundzada.

"If anyone goes outside of Afghanistan for the goal of jihad, it won't be called jihad," Akhundzada said, according to Mujahid.

"If the emir prevents the mujahideen (fighters) from going to battle and they still do it, this is war, not jihad."

The remarks come after Islamabad said militants behind a spate of suicide attacks in Pakistan were being helped by "Afghan citizens" across the border, days after a deadly bombing claimed by the Islamic State group near the countries' shared frontier.

Pakistan Prime Minister Shehbaz Sharif stopped short of accusing Afghanistan's Taliban government of knowingly allowing attacks from its soil, but he did say Pakistan militants were operating from "sanctuaries" in the neighbouring country.

Since the Taliban surged back to power in Afghanistan two years ago, Pakistan has witnessed a dramatic uptick in militant attacks focused on its western border regions, claimed by both Afghan Taliban ally Tehreek-e-Taliban Pakistan (TTP) and rival IS.

Formed in 2007 by Pakistani militants who splintered off from the Afghan Taliban to focus their fight on Islamabad for supporting America's invasion of Afghanistan, the TTP has since waged a bloody campaign of bombings and other attacks across Pakistan.

Afghanistan's Taliban authorities insist they do not allow the country's soil to be used by armed groups plotting against other nations.

In Islam, the Arabic term "jihad" is used to describe a wide range of religious struggles, from the private spiritual realm to taking part in combat.