The video comes just as Indonesia was already beginning to question the extent to which militant ideology had spread in the country.  Last week a dossier from the Australian Federal Police was leaked to the media alleging that two former commercial pilots had been posting pro-Isis material on social media and interacting with Indonesian fighters thought to have fled to the Middle East. Meanwhile, police are investigating an explosion last week in one of Jakarta's major shopping malls, which they suspect was linked to Isis.  While President Joko Widodo is preoccupied with slowing economic growth and political infighting, analysts say the extremist threat in the world's largest Muslim-majority nation has been growing in the past year, since the country's best known radical cleric, Abu Bakar Ba'asyir, swore allegiance to Isis from a high-security prison on Nusa Kambangan island, south of Java.  The previous government responded to rising support for Isis by formally banning the group and increasing monitoring of those travelling to Turkey and other countries that form a gateway to the Syrian conflict  But Mr Widodo, a former small-town mayor with scant experience in security and foreign policy, has done little to crack down further.  More from the Financial Times:  Indonesia investigates Isis link to pilots 4 US marines killed in 'terrorism' act The shifting face of terrorism in Britain  Ms Jones estimates there are now more than 300 Indonesians fighting with Isis in the Middle East. While this figure is dwarfed by the numbers leaving some European countries to join the militant group, it is larger than previously thought, raising concerns that returning jihadis could revive extremist cells back home — just as veterans of the Afghan war in the 1980s formed the al-Qaeda-sponsored Jemaah Islamiyah network behind a string of high-profile terrorist attacks across the region more than a decade ago.  Achmad Sukarsono, an analyst at the Eurasia Group, warns against underestimating the threat "because if a few Afghan veterans can create JI, what happens if 500 or more Indonesians come back from the Middle East theater and feel they need to do something in Indonesia?"  Analysts say Mr Widodo is too focused on other matters.  "The whole Islamic issue doesn't figure that high on his priority list," says Michael Buehler, a lecturer at London's School of Oriental and African Studies. "He has so many problems just basically surviving politically."  Stronger laws are required to enforce Indonesia's ban on Isis, according to the Institute for Policy Analysis and Conflict, as travelling overseas for military training is not illegal in Indonesia, while police struggle to curb the hate speech of radical preachers in a country where religious groups still wield considerable power.  In particular, the think-tank highlights the need for security forces to identify radical mosques, and for simple intervention in prisons, where jihadi inmates have held well publicized oath-taking ceremonies and regularly use mobile phones.  "There is an information system that goes through the prisons," explains Ms Jones. "People who want to go to Syria can go and visit someone in a maximum-security prison, get the contacts for one of his friends on the outside . . . and find a way of getting there.  Yet recent inaction may come down to widespread belief that the threat of terrorism in Indonesia has subsided in the past 15 years, with no major incident since nine people were killed in suicide bombings at major hotels in Jakarta six years ago.  Read MoreISIS leader killed, wife captured by US forces in Syrian firefight  Indonesia's militant groups had been left splintered since the country's US-funded counter-terrorism police cracked down on Jemaah Islamiyah after more than 200 people were killed in the bombing of a Bali nightclub in 2002. And the country ranked just 31st of 124 countries in the Global Terrorism Index published by the Institute of Economics and Peace last year, just below the US and above Israel.  Though returning jihadis could revive extremist cells in the country, Azyumardi Azra, a leading moderate thinker, claims Indonesian Muslims are largely tolerant and find the Wahhabi fundamentalism exported from the Middle East "too dry, too pure, too primitive, too Spartan".  "We are worried," he says. "But we are not scared."  However, Eurasia Group's Mr Sukarno says that to the moderate nature of the majority should not lead to complacency.  "In general the Muslim community in Indonesia is a lot more moderate than in the Middle East — but you don't need a community to be radicalized," he says. "You need a very few people."
Footage this week of Indonesian militants thought to be fighting in Syria for ISIS shocked Southeast Asian security analysts, the Financial Times reports.