'Wish You Were Here': Western Jihadis Unmask to Lure Others to Fight

Ex-military official: Fighters using US hummers for suicide bombings.

And that blunt invitation in the video from the Islamic State of Iraq and Syria is coming from English-speaking, unmasked jihadis cradling as many children in their arms as automatic weapons as they beckon their fellow Americans, Britains, Fins, Belgians and others to join the Muslim caliphate they've proclaimed there.

"Please O believers, come, who can make it, come. Come to Sham [Syria] as soon as possible," says an "mujahid" who claims to be American in the 30-minute video released last weekend, identified by his nom de guerre Abu Abdurahman al-Trinidadi.

Cradling an automatic weapon in one hand and a young boy in his other arm and standing on a street alongside other fighters with weapons who are also surrounded by kids, the Caribbean-accented al-Trinidadi added, "Look at all the little children -- they’re having fun."

US 'Extremely Concerned' About Jihadi Takeover of Iraq's Most Dangerous Dam

US Carries Out Airstrikes Against ISIS in Iraq

The Dramatic Gains ISIS Has Made in Iraq

The nine testimonials mark a turning point in the shocking evolution of ISIS, which had been allowed to grow into an army over the past two years with ambitions that have mushroomed beyond simply opposing the Syrian regime of Bashar al Assad in Damascus.

The westerners once under wraps are now openly beckoning their kind to the fight and giving western intelligence officials more jitters.

U.S. intelligence agencies and independent experts estimate that more than 12,000 foreign fighters have fought in Syria -- mostly Islamist extremists -- including thousands from Europe and more than 100 from the U.S. But they have mostly stayed in the shadows until ISIS blitzed Iraqi forces in the north this summer and announced an Islamic state or caliphate a few weeks ago.

"Ever since they announced that they have this caliphate, they've been more prominent about pushing out recruitment materials to non-Arabs. We've seen stuff in French and in German, as well as in English," Aaron Zelin, who researches foreign fighters at the Washington Institute for Near-East Policy, told ABC News Thursday. “It seems like they're not just trying to recruit people for military types of activities, but to have this functional state they need people with actual skills to come there.”

Old American Vehicles Used in Suicide Attacks

Counterterrorism officials in Europe and the U.S. have expressed grave concern over how easy it is to get to Syria, how hard it is for their agencies to track westerners traveling overland mostly through Turkey, and the likelihood that as many as half of their citizens who've gone to fight in Syria haven't been identified by name and could return home. The biggest fear are those willing to die to carry out attacks.

ISIS has focused its offensive this week on areas held by Kurdish peshmerga forces, who are badly outgunned, and the terror group is using military vehicles captured from Iraqi government forces as armored truck bombs -- in some cases driven by foreign fighters eager for matryrdom, said one retired top U.S. commander with close ties to Iraq.

"They're using American humvees as vehicle-borne improvised explosive devices to run up against the peshmerga lines. The Kurds have nothing to stop them -- just bullets," retired Army Lt. Gen. Michael Barbero, a former deputy commander of U.S. forces in Iraq, told ABC News.

Among the jihadis featured in the killer tourism video is a grinning Finnish fighter, who pledges that the caliphate "will expand to the whole world by Allah's permission," and that ISIS is "calling on all the Muslims living in the West, America, Europe and everything else to come."

"And here you go for fighting and afterwards you come back to your families. And if you get killed then you'll enter Jannah [paradise], insha'allah [Godwilling], and Allah will take care of the ones you've left behind," the fighter, identified as Abu Shuaib as-Somali, says.

The recent shift to putting westerners on camera, whose value previously has been their anonymity and potential ease of travel between Syria, Iraq and their home countries, may be an implied threat to western countries contemplating attacks on ISIS, said Robin Simcox, a terrorism researcher at the Henry Jackson Society in London.

Applying for Terror: Group Wants ‘Character References’

But ISIS also faces competition in its recruitment of westerners with their skills and passports from their weakened rival in the Syrian resistance, Jabhat al-Nusra, which is core al Qaeda's endorsed affiliate.

"Some people argue they're competing to attack the west. There clearly will be competition to recruit westerners," said Peter Neumann, a King's College researcher in London who directs field research which includes interviews of foreign fighters. Most of the westerners have joined ISIS, he said.

"A lot of westerners want to join Jabhat al-Nusra but are turned down, we've heard," Neumann told ABC News this week. "Jabhat al-Nusra has been much more selective about recruiting western fighters. They even want character references."

A 22-year-old Florida man, Moner Mohammad Abu-Salha, appeared posthumously in Jabhat al-Nusra videos posted online in late July, two months after U.S. officials confirmed he drove an armored truck bomb that detonated inside a Syrian regime military camp. He also traveled home to Florida before returning to Syria, officials say.

"We need to come and fight...whether you be in America, Britain, any place in the world right now," Abu-Salha said in a rambling half-hour video in which he praised slain Yemeni-American AQAP terror leader Anwar al-Awlaki and also warned President Obama that his days are numbered.

"The key thing they bring is their passport. If ISIS is looking to carry out attacks in the west and Europe, the western passports are very valuable. Not just sending people back to carry out attacks, but also to recruit others," Simcox said.

The jihadis in the ISIS video repeatedly reject the western life they grew up in and encourage those similalrly disaffected to journey to "al Sham."

"I don't think there's anything better than living in the land of Khilafah," said a British fighter calling himself Abu Abdullah al-Habashi. "You're not living under oppression."

CLICK HERE to return to the ABC News Investigative Unit homepage.