The leader of the Nigerian terror group Boko Haram has established the world’s second Islamic “caliphate” this summer and is seeking to cement his bloody rule on a territory that is now roughly the size of West Virginia.

While much of the world has been focused on the brutal reign of ISIS in Iraq and Syria, the forces of Boko Haram have been racking up victories in northern Nigeria and violently imposing an equally harsh version of Islamic law on approximately 3 million civilians – including beheadings, forced marriages and the forced induction of children into its military forces.

Most recently, the group’s fighters have seized two cities with a combined population of 600,000; nearly surrounded Maiduguri, home to about 1 million Nigerians; and sent government troops fleeing in scenes reminiscent of the rout of the Iraqi army by ISIS fighters this spring.

Tens of thousands of refugees have likewise streamed across the border with Cameroon, in some cases pursued by Boko Haram fighters. Islamist fighters also kidnapped the Cameroon’s deputy prime minister’s wife, who remains missing.

“Boko Haram is hacking at the roots of local governance in northeast Nigeria in an attempt to plant their brutal interpretation of Islamic law,” one U.S. official told NBC News on Friday. “In the process they are devastating local communities and exacerbating an already dire humanitarian situation present in Borno State."

The official said a new government report on Boko Haram had been prepared this week and distributed to policy-makers.

"Allah used us to captured Gwoza; Allah is going to use Islam to rule Gwoza, Nigeria and the whole world."

Boko Haram’s emir, Abubakar Shekau, spoke of the new Muslim state in an hour-long video released on Aug. 24, after the group seized Gwoza, a mostly Christian city of 300,000 on the border with Cameroon.

“Thanks be to Allah, who gave victory to our brethren in Gwoza and made it part of the Islamic caliphate,” he said on the video. “We did not do it on our own. Allah used us to captured Gwoza; Allah is going to use Islam to rule Gwoza, Nigeria and the whole world."

Shekau, a multilingual jihadi responsible for the deaths of thousands of his countrymen, also spoke of killing 1,000 "infidels" in the city on that day alone.

Although some analysts suggest that Shekau’s pronouncement fell short of a formal declaration of a caliphate -- an Islamic state led by a supreme religious and political leader known as a caliph – within Africa’s most populous nation, the group is for the first time attempting to seize and hold territory outside its base, according to U.S. analysts and experts.

John Campbell, a former U.S. ambassador to Nigeria, said Shekau appears to be partly following the lead of ISIS leader Abu Bakr al-Baghdadi.

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“Shekau likes to copy and mimic some aspects of ISIS and he was one of the few jihadi leaders who welcomed ISIS’s declaration of a caliphate in Iraq and Syria,” he said.

J. Peter Pham, the head of the Atlantic Council's Africa Center, noted that Shekau also claims to have previously spoken with al-Baghdadi, though he said the communications between the two groups has apparently been mostly the sharing of "best practices" on military strategy and bomb-making over social media.

"That was our safe haven, our front line. Now, it's much more difficult for us to tell the story."

Unlike the U.S. response to ISIS, an expanding air campaign that is expected to soon target that group’s leadership and heavy weapons, Washington’s response to Boko Haram has been low-key. It is providing limited logistic and intelligence help for the Nigerian military, and last week announced a border-security program aimed at preventing the group from threatening Nigeria's neighbors. U.S. rhetoric has also been controlled and delivered in out-of-way settings, not by the president in a nationwide broadcast from the White House.

Emmanuel Ogebe, a Nigeria human rights lawyer, said one reason that there is so little interest in the conflict is that there are virtually no international media or aid and human-rights workers left in the region.

"When the town of Michiko in Adamawa province fell last weekend, it was the last bastion of human rights workers, our staging area,” he said. “We were not allowed to stay overnight beyond that city. That was our safe haven, our front line. Now, it's much more difficult for us to tell the story."

Linda Thomas-Greenfield, the U.S. assistant secretary of state for African affairs, visited the Nigerian capital of Abuja last week for a meeting of the U.S.-Nigeria bilateral working group. In remarks afterward, she said the threat was expanding.

"Since our last meeting in August 2013, the frequency and scope of Boko Haram's terror attack have grown more acute and constitute a serious threat to this country's overall security," she said. "Boko Haram has shown that it can operate not only in the northeast but elsewhere in the country."

In many ways, ISIS and Boko Haram have followed similar paths. Like ISIS, Boko Haram has seized modern military equipment from the Nigerian army and sent government soldiers running for their lives after throwing down their arms. They've brutally killed thousands, beheading men who've refused to convert to Islam and forced their widows into marriage with Boko Haram soldiers, said Pham, acknowledging that some of the information is second-hand.

And although Boko Haram has not seized a large city like Mosul, which has a population of 1 million, as ISIS did in Iraq, that could change in a matter of days.

Boko Haram has now nearly surrounded Maiduguri with a pincer movement, and took control of the gateway city of Bama, another city with a population of nearly 300,000, last week.

"We are very troubled by the apparent capture of Bama and the prospects for an attack on and in Maiduguri which would impose a tremendous toll on the civilian population," said Thomas-Greenfield, in what was widely seen in a Abuja as a warning to the government of President Goodluck Jonathan. "This is a sober reality check for all of us. We are past time for denial and pride.”

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Pham said the situation has indeed worsened this week. Moreover, he said, the Nigerian government has lied about its successes and its failures, claiming erroneously that the army had reached Bama and was planning to liberate it.

"Despite claims that they've reached Bama, they have not,” he said. “… There is in fact a slapstick of video of Nigerian military literally fleeing Boko Haram in a comedic fashion. Meanwhile, we have the military claiming they're in control."

Pham, who regularly speaks with Nigerian security sources, said as many as 3,000 Nigerian soldiers recently dropped their weapons and fled over the border to Cameroon, where they remain.

Ogebe, the human rights lawyer, says the situation is so bad that the Nigerian public sees the terrorist group as more reliable than their own government.

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"It's a twilight zone, listening to the federal government while waiting for the terrorists to release the videos for the truth," said Ogebe.

The U.S. official made it clear that Washington doesn’t yet see Boko Haram in the same light as ISIS, in part because of the way the latter is serving as a magnet for jihadis around the world.

“Boko Haram isn’t ISIL," he said, using an alternative acronym for the Islamic State of Iraq and Syria. "Their foreign fighter recruitment is not as extensive, and they aren’t yet as adept at competently governing the areas they control. However, no one should take them lightly. Their violent track record, and aspirations are creating havoc in northeast Nigeria and threaten to further destabilize the region.”