In a region of fractured alliances, the merger announced Wednesday could allow the Islamic State of Iraq and Syria (ISIS) to control both sides of the border. The well-financed ISIS had seized Abu Qaim on the Iraqi side of the border earlier this week. Albu Kamal sits just opposite it, in Syria.

After months of clashes between ISIS and al Qaeda's al Nusra Front in Syria, Nusra's Albu Kamal branch "pledged loyalty to ISIS," Rami Abdel Rahman, the director of the Syrian Observatory for Human Rights said on Wednesday. "They are rivals, but both groups are jihadist and extremists," Abdel Rahman added. "This move will create tension now with other rebel groups, including Islamists, in the area."

Although both groups began as offshoots of al Qaeda, they became rivals after ISIS became involved in Syria's civil war in 2013. The central leadership of al Qaeda disowned ISIS and proclaimed the Nusra Front as its official affiliate in Syria.

In its efforts to create an Islamic state straddling both countries, ISIS has captured swathes of Iraq, beginning June 10 with Mosul, the main northern city. ISIS also controls large parts of eastern Syria, where it has clashed with rival rebels groups and occasionally fought alongside them, complicating the three-year-old insurgency against President Bashar al-Assad.

Omar Abu Leyla, a rebel spokesman in Syria's Deir Ezzor province, warned that "Albu Kamal is a red line." If ISIS fighters cross over from Iraq, he said, the opposition "Free Syrian Army will fight them."

'A coup'

Though ISIS and al Nusra appear to have put some differences aside, Prime Minister Nuri al-Maliki has rejected calls for such solidarity in Iraq, saying Wednesday that he would not respond to demands to form a unity government. The recent ISIS offensive has put pressure on Maliki from domestic opponents and international leaders. Critics have alleged that his policies are sectarian.

"The call to form a national emergency government is a coup against the constitution and the political process," Maliki said Wednesday in a televised address. "The dangerous goals of forming a national emergency government are not hidden," he added. "It is an attempt by those who are against the constitution to eliminate the young democratic process and steal the votes of the voters."

Maliki‘s State of the Law electoral bloc won the most seats in April's parliamentary elections, but, with just 92 of 328, it fell far short of a majority in Iraq's Council of Representatives, and he has had to ask the support of rivals in order to form a government. In office since 2006, Maliki needs the support of a simple majority in the chamber to hold on to the job for another four-year term.

Many have speculated that fighting in Iraq and Syria could destabilize the region. German Foreign Minister Frank-Walter Steinmeier has warned countries not to get involved in a proxy war.

mkg/ rc(Reuters, AFP, dpa, AP)