BEIRUT -- A Sunni extremist group in Syria took over opposition-held areas of a provincial capital near the border with Iraq on Monday after expelling rival fighters from an al-Qaeda-linked group, activists said.
The march by militants of the Islamic State group on the city of Deir el-Zour brings them closer to a showdown with President Bashar Assad's forces. They recently captured cities and towns in northern Iraq and merged them with much of the territory under its control in eastern Syria.
The Britain-based Syrian Observatory for Human rights said militants from IS took over the area from fighters of the rival al-Qaeda-linked Nusra Front group, who withdrew after clashes.
The new developments effectively expand and consolidate areas held by fighters from the Islamic State group in territory straddling the border between the two conflict-ridden countries of Syria and Iraq.
The group, which now controls large parts of northern Syria, is almost in full control of oil-rich Deir el-Zour province in the east, stretching from the Syrian border town of Boukamal to the provincial capital to the northwest. Assad's forces still control half of Deir el-Zour city, and no fighting between his troops and the extremist group was reported there.
Led by an ambitious Iraqi militant known as Abu Bakr al-Baghdadi, the Islamic State group unilaterally declared the establishment of an Islamic state, or caliphate, in the lands it has seized in Syria and Iraq. It proclaimed al-Baghdadi the head of its new self-styled state and demanded that all Muslims pledge allegiance to him.
Most significant Syrian rebel groups that have been fighting to overthrow Assad have rejected al-Baghdadi's declaration. The rebel groups, including the Nusra Front, have fought the extremist group since the beginning of the year. Nearly 7,000 people, mostly fighters, have died in the infighting, and tens of thousands of civilians have been forced from their homes.
However, Nusra Front appears to be losing the war within a war in Syria as fighters allied with powerful tribes in the country's east defect to al-Baghdadi's group.
The Syrian conflict began in March 2011 as largely peaceful protests against Assad's rule, but turned into an armed revolt after some opposition supporters took up weapons to fight a brutal government crackdown on dissent. It deteriorated into civil war in which Islamic extremists, including foreign fighters and Syrian rebels, who have adopted hard-line al-Qaeda-style ideologies, have played an increasingly prominent role among the fighters, dampening the West's support for the rebellion.
Also Monday, the U.N. Security Council unanimously approved a resolution authorizing cross-border delivery of desperately needed food and aid to Syrians in rebel-held areas, without government approval.
The resolution expressed "grave alarm at the significant and rapid deterioration of the humanitarian situation in Syria" and deplored the fact that its previous demands for humanitarian access "have not been heeded" by the Syrian government and opposition fighters.
The council adopted a resolution in February demanding that all sides in the conflict allow immediate access for aid, lift the sieges of populated areas, stop depriving civilians of food and halt attacks against civilians. But monthly reports to the council since then by U.N. Secretary-General Ban Ki-moon on its implementation have described an increasingly dire situation.
Just hours before the resolution was adopted, some 13 Syrian Red Crescent trucks loaded with 1,000 food parcels crossed into the rebel-held Damascus suburb of Moadamiyeh, which has been besieged by government troops for more than two years, causing widespread hunger-related illness and death among its residents.
In Yarmouk, a Palestinian refugee camp in Damascus that has been under government siege for over a year, U.N. aid workers were not allowed to distribute aid on Monday, UNRWA spokesman Chris Gunness said in a statement, adding that 18,000 civilians remain trapped there in desperate need of food and medicine.
The interruption follows a week of sustained food distribution in Yarmouk during which the U.N. agency that helps Palestinian refugees in the Middle East distributed food parcels to 3,316 families, Gunness said.
Associated Press writer Albert Aji in Damascus, Syria, and Bassem Mroue in Beirut contributed to this report.
