Islamist groups around the world have hailed the Taliban's takeover in Afghanistan, sparking global alarm that the country could once again become a safe haven for jihadists inspired by its success.
The Taliban have said they will not allow Afghanistan to be used to launch attacks on other nations.
But experts say that ties remain with al Qaeda, whose attacks against the United States prompted Washington to invade the country in 2001, as well as other militant groups including in neighbouring Pakistan.
One of the Taliban's top leaders is Sirajuddin Haqqani, the head of the militant Haqqani network. The United States has designated him a global terrorist and offered $5 million for information leading to his arrest.
"Jihadists writ large are jubilant and electrified by the Taliban's return," said Asfandyar Mir, a South Asia security scholar affiliated with Stanford University's Center for International Security and Cooperation.
"Major jihadist constituencies across South Asia, Middle East and Africa have taken note ... (and) al Qaeda's eco-system sees the Taliban's return as its own victory."
Besides groups affiliated to al Qaeda, congratulatory messages to the Taliban have come from Somalia's al-Shabaab and Palestinian groups Hamas and Islamic Jihad.
Yemen's Shi'ite Muslim Houthi group, which is opposed to the United States and other Western countries, said events in Afghanistan proved that foreign "occupation" was bound to fail.
The Pakistani Taliban, which is not part of the Afghan group, pledged allegiance, and said hundreds of its members were freed from prisons when the Afghan Taliban swept through the country in recent days.
World leaders have been sceptical of the Taliban's moderate public pronouncements since seizing power, although some diplomatic officials familiar with its negotiations say the group is seeking international recognition and possibly development assistance.
Zabihullah Mujahid, the group's spokesman, promised at a news conference in Kabul on Tuesday that Afghanistan would not be used to launch any attacks on foreign countries.
"I would like to assure the US and the international community that no one will be harmed ... we will not allow our territory to be used against anybody," he said. "We don't want any internal or external enemies."
ISLAMIC STATE
Independent UN experts reported to the Security Council last month that al Qaeda was present in at least 15 of Afghanistan's 34 provinces.
The experts also said Islamic State had expanded its presence to several provinces, including Kabul, and that fighters has formed sleeper cells.
Islamic State is opposed to the Taliban. But some analysts and officials cautioned that the ultra-radical group could take advantage of any chaos, or encourage hardline Taliban fighters to defect as the movement settles into governance.
UN Secretary-General Antonio Guterres has appealed to the Security Council to "use all tools at its disposal to suppress the global terrorist threat in Afghanistan."
The Security Council stressed the importance of combating terrorism in Afghanistan to ensure other countries were not threatened or attacked.
In a call with US President Joe Biden, British Prime Minister Boris Johnson "stressed the importance of not losing the gains made in Afghanistan over the last 20 years, of protecting ourselves against any emerging threat from terrorism," a Downing Street spokesperson said.
Two sources familiar with the matter said China had raised concerns over the anti-China East Turkestan Islamic Movement(ETIM) group with the Taliban in recent meetings.
"They have been taking up the issue of ETIM whenever they call on us," a Taliban source told Reuters, saying the group reassured China they would not allow attacks to take place.
The US government says ETIM no longer exists as a formal organization and is instead a broad label China uses to oppress a variety of Muslim ethnic groups, including Uyghurs, in its Xinjiang region. China denies all accusations of abuse.
RISK TO PAKISTAN
The most concrete risk, some officials and analysts say, is to Afghanistan's neighbour Pakistan.
"The first, easy test of their commitment (to their promises) is the TTP," said Mir at Stanford University, referring to the Pakistan Taliban.
"Based out of eastern Afghanistan ... the TTP has stepped up violence against Pakistan and appears to be preparing for a major campaign."
The TTP said that 780 of their members, including former second-in-command Maulvi Faqir Muhammad, have been freed from prisons in Afghanistan, and had made their way to what the group called its strongholds in eastern Afghanistan.
An Afghan Taliban spokesman did not immediately respond to requests for comment on the prisoner release.
At their peak, Pakistani Taliban attacks killed hundreds of people, including one assault on a school in Peshawar in 2014 that killed more than 140 people, most of them children.
TTP operations were severely disrupted in subsequent years, but more recently has begun to regroup and launched attacks on ecurity personnel in border areas.
Georg Riekeles, associate director of the European Policy Centre think-tank in Brussels, said the Afghan Taliban wanted international recognition and could try to live up to their promise to not allow Afghanistan to become a base for militancy.
But he said the Taliban's success had made them heroes to the Islamic radical underground.
"You find all the ingredients of the myth that inspires and draws extremist groups and youth: radical religious ideology, heroic fighters in rugged mountains, military success and victory first against Soviet invasion, now against the US.
"That's part of the lessons we must draw, and what we must prepare for."
