Over 50 militants have been killed in the air strikes but the attacks have failed to halt the Islamic State of Iraq and al-Sham (ISIS) militants' advance toward the Syrian capital, according to the Syrian Observatory for Human Rights. The militants have already seized key phosphate mines as they move south toward Damascus, extending their control over Syria's resources. "ISIS has made further progress on the Tadmor-Damascus highway and grabbed the Khnaifess phosphate mines (70km south of Palmyra) and nearby houses," said the Observatory. "It has extended its control over larger areas and even greater economic interests," it added.

ISIS has already seized Syria's main oil and gas fields, which are located in the Deirez Zor province near the Iraq border. The latest mines seized by ISIS, which lie just 140km north of Damascus are the second largest in the country. In the first half of 2014, the General Company for Phosphate and Mines reported sales of $30 million on production of almost 500,000 tons, down from two million tonnes in 2011. Syria is considered to have one of the world's largest phosphate reserves. "With the suspension of oil exports, phosphates represented one of the last sources of income of the state," according to Syria Report, an online business weekly. ISIS is accused of executing hundreds of people in and around Palmyra since it swept into the oasis city last week after a lightning advance across the desert from its stronghold in the Euphrates Valley to the east.

The Observatory said on Sunday that it had documented the executions of at least 217 people, among them 67 civilians, including 14 children. Some of those killed had been beheaded, Observatory director Rami Abdel Rahman said, adding that the militants had also taken some 600 people prisoner. Syrian state media said at least 400 civilians had been killed by ISIS in Palmyra, most of them women, children and old men. In Syria, military forces said more than 160 ISIS targets have been struck, killing and wounding terrorists and destroying weapons and vehicles equipped with machineguns" on Palmyra's outskirts and elsewhere in the east of Homs province. The Syrian Observatory for Human Rights said at least four civilians had been killed in the raids, which were the most intense since the militants overran the city on Thursday. Dozens of people had also been wounded in the raids, and ISIS was believed to have taken losses when a military security building was hit, said Observatory director Rami Abdel Rahman. The strikes targeted several areas of the city, including some close to the city's famed Graeco-Roman ruins, a UNESCO world heritage site, he said.

ISIS also made advances in Iraq as the militant group surprisingly captured Ramadi two weeks ago. Iraq on Tuesday announced the launch of a military operation to drive ISIS out of Ramadi. A spokesman for Iraq's Shiite militias said the operation will "not last for a long time" and that Iraqi forces have surrounded the provincial capital, Ramadi, from three sides.