Al-Qaeda is still "heavily embedded" within the Taliban in Afghanistan, in spite of a historic US-Taliban agreement earlier this year, a senior United Nations official has told the BBC.
Earlier this year, the US signed an agreement with the Taliban committing to withdrawing all American forces from the country by next summer if the Taliban ensured groups including al-Qaeda were not able to use Afghan territory to plot international attacks.
But Edmund Fitton-Brown, co-ordinator of the UN's Islamic State, Al-Qaeda and Taliban Monitoring Team, has told the BBC that the Taliban promised al-Qaeda in the run-up to the US agreement that the two groups would remain allies.
"The Taliban were talking regularly and at a high level with al-Qaeda and reassuring them that they would honour their historic ties," Mr Fitton-Brown said.
He said the relationship between al-Qaeda and the Taliban was "not substantively" changed by the deal struck with the US. "Al-Qaeda are heavily embedded with the Taliban and they do a good deal of military action and training action with the Taliban, and that has not changed," he said.
Eliminating the threat from al-Qaeda and overthrowing the Taliban regime that had harboured them was the original basis for the US invasion of Afghanistan, following the 9/11 attacks. At the time, President George W Bush vowed to hunt the militants until there was "no place to run, or hide, or rest".
Al-Qaeda's strength and ability to strike the West has significantly diminished over the past decade, but its leader Ayman al-Zawahiri is believed to still be based in Afghanistan along with a number of other senior figures in the group. The Afghan intelligence services announced on Saturday they had killed Husam Abd al-Rauf, a high ranking Egyptian al-Qaeda member, in an operation in Ghazni province. Mr Fitton-Brown told the BBC that despite its lower profile, al-Qaeda remained "resilient" and "dangerous".Taliban officials have insisted that they will fully adhere to the conditions of their agreement with the US: preventing any group from using Afghan soil as a base to plan attacks against the US and its allies. The insurgents say they aim only to implement an "Islamic government" within Afghanistan, and will not pose a threat to any other country.
The Taliban has also highlighted its fight against Islamic State group militants as an example of its commitment against other extremists. But the Taliban regard IS as rivals, whereas they have had a close relationship with al-Qaeda since that groups' inception.
Mr Fitton-Brown said he had noted recent reports about the Taliban requiring some Pakistani foreign fighters in Afghanistan to register with them and abide by a code of conduct forbidding attacks outside Afghanistan. Mr Fitton-Brown said it was not yet clear whether that agreement applied to al-Qaeda, nor whether it was an "irrevocable" move toward preventing foreign militants posing a threat internationally from Afghanistan.