Little known to the wider world 18 months ago, the Islamic State extremist group has muscled its way into the international spotlight by carving out a self-declared caliphate in the heart of the Mideast, beheading its opponents and foreign journalists, and attracting radicalized youth as far afield as Paris, London and New York.

The militants' once seemingly unstoppable push across Syria and Iraq has slowed to a crawl in recent months as the United States, its Arab allies and even rival Iran work to roll back the group and ultimately defeat it. Despite those efforts, the extremists show little sign of crumbling under the weight of international efforts to crush it.

Here's a look at what happened this week involving the extremist group and the fight against it:

SYRIA AND IRAQ: KIDNAPPING CHRISTIANS AND SMASHING ANCIENT ARTIFACTS

In northeastern Syria, the militants swept through several villages and seized more than 220 Christians from their homes over a three-day stretch beginning around dawn Monday. The onslaught also forced thousands of people to flee to nearby cities. The fate of those kidnapped, almost all of them Assyrian Christians, remains unclear. The abductions have compounded fears among religious minorities in both Syria and Iraq, where the Islamic State group's fighters have repeatedly targeted minorities, killing them, driving them from their homes, enslaving their women and destroying their places of worship.

In northern Iraq, meanwhile, the militants took sledgehammers and drills to smash ancient Mesopotamian statues and other artifacts in the city of Mosul, including a winged-bull that dated to the 7th century B.C. The destruction, documented in a video posted online, is part of a wider campaign by the extremists to eliminate anything that they view as heretical. UNESCO's director general, Irina Bokova condemned the destruction, calling it "a deliberate attack against Iraq's millennial history and culture" and "an inflammatory incitement to violence and hatred."

LONDON TO SYRIA: THREE SCHOOLGIRLS LEAVE HOME TO JOIN THE MILITANTS

The long reach of the Islamic State group was felt in London this week with the news that three teenage girls had left their families with the apparent intent of joining a friend who already was with the extremists in Syria. It was another indication that IS had at least some appeal to a small number of Britons who may believe propaganda videos posted online about the building of a caliphate in Syria and Iraq.

The CCTV photos of casually dressed Shamima Begum, 15, Kadiza Sultana, 16, and Amira Abase, 15, leaving London's Gatwick Airport on a Turkish Airlines flight to Istanbul captivated Britain for days. The girls' distraught families issued urgent, tearful pleas imploring the girls to turn back once they arrived in Turkey rather than entering Syria. Prime Minister David Cameron warned that every school and college in Britain needs to play a role in stopping people from joining what he called "an appalling death cult."

The search proved fruitless. London police said Tuesday that their information indicated the girls had successfully crossed into Syria, where they are thought to have linked up with the Islamic State group. Officials say 500 to 600 Britons have traveled to Syria to help the militants, with an increasing number of young women showing an interest in the group.

JIHADI JOHN'S IDENTITY REVEALED: BRITISH SECURITY HAD QUESTIONED THE MAN BEHIND THE MASK YEARS AGO

The masked militant known as "Jihadi John" who has played a prominent role in Islamic State beheading videos was revealed this week to be Mohammed Emwazi, a Kuwait-born computer scientist who had moved to London with his family as a young boy. He had not been known to the general public, but had been seen by Britain's security services as a potential threat. It turned out they had questioned him several years ago — and, according to emails Emwazi sent to an Islamic support group, even tried to recruit him as an informer.

The case highlighted the difficulties Britain faces in trying to mitigate the terrorist threat. Security officials had questioned Emwazi because they believed he had been planning to join a terrorist group in Somalia, but he still was able to leave Britain and join militants in Syria. Cameron defended Britain's intelligence services, but Emwazi's ability to travel freely to Syria is seen as an indication that British police and security forces are simply overwhelmed by the number of people who are radicalizing.

UNITED STATES TO SYRIA? AMERICAN AUTHORITIES ARREST THREE MEN ACCUSED OF PLOTTING TO HELP MILITANTS

The Islamic State group's ability to inspire devotion allegedly reached the United States as well, where authorities arrested three men Wednesday on charges of plotting to help IS and wage war against the U.S.

Akhror Saidakhmetov was arrested at New York's Kennedy Airport, where he was attempting to board a flight to Istanbul en route to Syria. Abdurasul Hasanovich Juraboev had a ticket to travel to Istanbul next month. The third defendant, Abror Habibov, was arrested in Florida and stands accused of helping fund Saidakhmetov's efforts.

Prosecutors say Saidakhmetov, 19, also threatened an attack in the U.S. if he was unable to join the Islamic State group. Juraboev's plans included attacks against U.S. President Barack Obama or planting a bomb on Coney Island, officials said.

For the past year, the FBI has expressed worries about the flow of Western fighters to Syria. The Department of Justice has charged around 20 people in the past year with planning to travel to the Middle East to fight alongside militants, including from IS. U.S. officials are concerned about Americans going overseas to train with these groups and returning with plots to carry out attacks at home.

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Associated Press writer Gregory Katz in London contributed to this report.

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Follow Ryan Lucas on Twitter at www.twitter.com/relucasz .