BAGHDAD (CBS News/CBSDC/AP) — Fresh from success in Iraq, a Sunni extremist group tried to tighten its hold Wednesday on territory in Syria and crush pockets of resistance on land straddling the border where it has declared the foundation of an Islamic state.

Embattled Iraqi Prime Minister Nouri al-Maliki warned that the entire region is endangered by the Islamic State of Iraq and Syria, known as ISIS, whose gunmen have rampaged across his country in recent weeks. Facing pressure to step aside, al-Maliki said the focus must be on countering the threat – not wholesale leadership changes.

The militant group has fed off the chaos and supercharged sectarian atmosphere of Syria’s civil war to seize control of a large chunk of territory there. With its recent blitz across Iraq, it has expanded its gains while also effectively erasing the border between the two countries and laying the groundwork of its proto-state.

Led by an ambitious Iraqi militant known as Abu Bakr al-Baghdadi, the group this week unilaterally declared the establishment of an Islamic state, or caliphate, in the land it has seized. It also proclaimed al-Baghdadi the head of its new self-styled state governed by Shariah law and demanded that all Muslims pledge allegiance to him.

Its assault in Iraq appears to have slowed after sweeping across the predominantly Sunni Arab areas and encountering stiff resistance in Shiite-majority regions. But in Syria, al-Baghdadi’s group has forged ahead with an offensive against towns and villages held by rival rebels along the Euphrates River in the eastern province bordering Iraq.

Militants stormed houses in the frontier town of Boukamal, rounding up people suspected of opposing them, the Britain-based Syrian Observatory for Human Rights said. The extremist group captured Boukamal on Tuesday, after fighters from the al Qaeda-linked Nusra Front defected.

Al-Baghdadi’s fighters also were battling rival factions at the northern entrance to the nearby town of Sheheil, a Nusra Front stronghold, forcing thousands of residents to flee.

The group is reviled by most Syrian rebel groups, and many of them have been locked in a bloody six-month battle with it across northern Syria that has killed more than 7,000 people. A few smaller rebel factions have pledged loyalty to al-Baghdadi’s organization out of fear or convenience, but most factions in Syria oppose it.

On Wednesday, nine Syrian rebel groups, including a powerful coalition called the Islamic Front, rejected al-Baghdadi’s declaration of a caliphate. In a statement posted on Islamic websites, they said the declaration was “void” and pledged to continue the fight.

In Raqqa, the Syrian stronghold of al-Baghdadi’s group, activists said the extremists displayed more heavy weaponry believed to have been looted from Iraqi military bases.

Video posted by activists showed what appeared to be an Islamic State leader asking a group of people in a mosque, including children, to pledge loyalty to al-Baghdadi. The video appeared genuine and corresponded to other Associated Press reporting.

“Before, it was enough if you showed them support; now they’re asking people to swear allegiance,” said a Raqqa-based activist who spoke condition of anonymity because he fears retribution. He and other activists said the group also was punishing and jailing people suspected of breaking the traditional dawn-to-dusk fast for the holy month of Ramadan, which began Sunday.

In his weekly address, Iraq’s prime minister warned that the group’s self-proclaimed caliphate meant “no one in Iraq or any neighboring country will be safe from these plans.” The group’s declaration was “a message to all the states in the region that you are inside the red circle now,” al-Maliki said.

The failure of al-Maliki’s Shiite-led government to promote reconciliation is being blamed for fueling the Sunni insurgency. Sunnis and Kurds, both of whom accuse him of breaking promises and trying to monopolize power, demand that he be replaced.

Al-Maliki did not directly address calls to step down, but he did say the focus should be on turning back the militants – and not political changes.

“The priority today in the battle is security and the security challenges and the plots being formed by the terrorist organizations leaning on a sectarian program. The battle today is first before everything,” he said. “It is a battle for security, a battle to protect Iraq, and Iraq’s unity and identity, and the identity of the public and their security and economy.”

The new parliament met Tuesday for the first time since April’s elections amid hopes for the swift formation of a government. But lawmakers deadlocked less than two hours into the meeting, and Sunnis and Kurds walked out.

While Sunni insurgents and Shiite forces fight for control of Iraq, in the north, the Kurds are making their own moves.

Kurdish troops, known as the Peshmerga, have been reinforcing defenses and raising their flag outside the city of Kirkuk, CBS News’ Charlie D’Agata reported.

The Peshmerga quickly took over the oil-rich city in the wake of the ISIS advance when Iraqi troops abandoned the city.

Masoud Barzani, the president of the Kurdish regon, has announced the Kurds will hold their own vote for independence.

The Kurds live in a relatively prosperous and stable region in northern Iraq built on oil money.

The relationship with the central government in Baghdad has never been a close one. Now they’d like to separate altogether.

Al-Maliki said Wednesday that would be illegal.

The United States and Iraq’s regional neighbors Turkey and Iran — both of which have large Kurdish minorities — are opposed to Kurdish independence.

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