Marched on to a Libyan beach in now gruesomely familiar orange jumpsuits, the last moments of 21 Coptic Christians carried the vicious jolt of previous Isis snuff videos, but with an added charge of fear.

The setting, in Libya, suggested that the group was spreading further and faster than even their dramatic early advances seem possible, and it came after vows of allegiance to Isis leader Abu Bakr al-Baghdadi by militants from Afghanistan to Yemen.

“With affiliates in Algeria, Egypt, Libya, the group is beginning to assemble a growing international footprint,” Marine Corps Lieutenant General Vincent Stewart, director of the Defence Intelligence Agency, warned the US House of Representatives this month.

The beheading of a tourist in Algeria, a meticulously videoed attack on an Egyptian army base, including the casual murder of surviving soldiers, a suicide bombing in Tripoli’s smartest hotel – all were recently masterminded by militants publicly loyal to a group whose name once defined its geography: “Islamic state in Iraq and Syria”.

Affiliates are adopting their slick media production along with bloody tactics, amplifying the influence of the violence. The murder of the Egyptian Christians has already drawn bombing raids on Libya by Egyptian jets, which may suit some Isis commanders keen to draw enemies into an expensive and draining war.

There are echoes of al-Qaida’s global expansion, even as its leader shrank into hiding, through loyal but virtually autonomous units in Yemen, north and east Africa, and other areas. But al-Qaida expanded slowly and carefully, vetting would-be allies that wanted to use its terrifying brand in their own battles.

Isis by contrast has already welcomed several would-be supporters under what seems to be a looser umbrella, among them Afghan fighters whom analysts say have significant theological differences with the group.

“I think it’s important for us to differentiate between the spread of Isil and individuals who are trying to attract attention for themselves by claiming an association with Isil,” said White House spokesman Josh Earnest. “Those are two very different things. And I think the best example we have of this is the situation that we saw in Afghanistan.”

The wealth Isis commands, the extraordinary power of its brand, and its dramatic sweep from obscurity to power over large swathes of two nations make it an alluring patron. It can offer support in areas from financial to weapons supply to practical assistance with video productions, and has more than proved its attraction to potential foreign donors and fighters. Isis arrived in Egypt effectively overnight, when local insurgent group Ansar Beit al-Maqdis pledged allegiance to Abu Bakr al-Baghdadi in November. The group has several years’ experience fighting Cairo’s forces and perhaps 12 million pieces of weaponry hidden in the vast deserts there, according to one former intelligence official.

In Libya, where Isis now controls three towns, its roots are less clear, with some fighters signing up from a homegrown militia based in Benghazi city, and others returning from Syria. The group has advanced quickly though across a country rocked by civil war, highlighting its progress with regular displays of extreme violence.

Countries bordering the Isis heartland are worried that it will try to infiltrate their territory. Lebanon’s security chief warned earlier this month that Isis is seeking control of villages along the border with Syria to use as staging posts for operations.

“Islamic State does not want to dominate Qalamoun … but they want to use it to secure their backs in the region,” Major General Abbas Ibrahim, head of Lebanon’s General Security Office, told Reuters recently. “The Lebanese military and security forces are on full alert.”

Beyond the immediate reach of Isis funds or tacticians, the group’s name has become so famous that it may have an attraction for those with an interest in its policies.

In January this year, after a steady trickle of reports from Afghanistan that Taliban commanders were signing up to join Isis, the group officially announced its first outpost beyond the Arab world, in “Khorasan”, an ancient name for Afghanistan and Pakistan.

Many analysts were sceptical that Afghan commanders declaring their loyalty were doing anything more than pursuing local rivalries with the latest tool to hand. They have so far avoided the sectarian atrocities that Isis has embraced in Iraq and Syria, and in some places are even reluctant to fly the black flag of the group they claim to serve.

“In practice, the IS groups in Helmand and Farah have not been involved (so far) in actions that resemble the brutality or sectarianism of the mainstream Isis,” said Borhan Osman, who has researched the group for the Afghanistan Analyst Network, and pointed out the theological disputes.

Isis could boast one Afghan commander with real links to the Isis heartland, a former Guantánamo detainee, but he was killed by a drone strike in January.

“Launching a militant offshoot in an unfamiliar land is one thing, seeing it grow into a solid force and sustaining it is another,” Osman wrote, in a recent paper about the group, that warned against exaggeration. “Afghanistan and Pakistan are a long way from the group’s heartland and it may have miscalculated its appeal.”

The Guardian