Al Qaeda-linked militants justified their takeover of a strategic opposition-held town near the Syrian border with Turkey by accusing the Syrian rebels who held it of being pro-democracy traitors who cooperated with Western officials like U.S. Sen. John McCain.
The ousted rebels "have called for democracy ... which conflicts with Islamic teachings," the Islamic State of Iraq and Syria announced in an online statement Monday.
ISIS said it "cleansed" the northern border town of Azaz of more moderate fighters from the rebel Free Syrian Army in the past week because the rebels "received American Senator McCain and agreed with him to fight Islamists."
Earlier this year, McCain made a surprise visit to this border region to lend support to Syrian rebels.
FSA rebels have controlled Azaz and the Syrian side of the Oncupinar-Bab el Salama border crossing with Turkey since seizing the town from the government of President Bashar al-Assad last year.
ISIS militants attacked the Syrian rebels and drove them out of Azaz after the rebels refused to hand over a German doctor that the al Qaeda-linked group accused of being a Western spy.
The deadly power play by ISIS left at least one prominent Syrian opposition activist from Azaz dead. The militant group also detained dozens of other anti-Assad fighters and activists, some of whom still remain in ISIS custody.
ISIS' ranks are bolstered by foreign jihadi militants from North Africa, the Caucasus and Iraq.
The group was denounced by the Syrian National Coalition, a Western-backed opposition group that operates largely in exile.
"ISIS no longer fights the Assad regime," the coalition declared in a statement published Friday. "Rather it is strengthening its positions in liberated areas at the expense of the civilians. ISIS is inflicting on the people the same suppression of the Baath Party and the Assad regime."
But it is unclear how much the coalition can dictate events on the ground inside Syria, where the north of the country is controlled by an assortment of rebel factions that often compete for weapons, territory and financial resources.
The Bab al Salama border gate is one of the main conduits for international aid to the opposition-controlled enclave in Northern Syria. International aid organizations have established logistical offices in the nearby Turkish city of Gaziantep to coordinate deliveries of badly needed food and medical supplies to millions of displaced Syrians.
The U.S. State Department has used the gate for previous shipments of what it describes as "non-lethal aid" to Syrian rebels.
The ISIS statement included a sharp warning to members of the Syrian opposition who work with Western governments and organizations.
"Those who cooperate with the Americans will be treated like them as per the holy Koran," ISIS announced.
Several hundred FSA fighters still control the customs terminal at the border gate leading to Turkey. However, eyewitnesses tell CNN that ISIS militants now control the town of Azaz, located less than a five-minute drive away.