The notion that young women are traveling to Syria solely to become "jihadi brides" is simplistic and hinders efforts to prevent other girls from being radicalized, new research suggests.

Young women are joining the so-called Islamic State group for many reasons, including anger over the perceived persecution of Muslims and the wish to belong to a sisterhood with similar beliefs, according to a report released Thursday by the Institute for Strategic Dialogue and the International Center for the Study of Radicalization at King's College London.

Al-Qaida-affiliate al-Nusra Front chief vowed in a wide-randing televised interview late Wednesday to defeat Hizbullah in al-Qalamoun.

Without showing his face, Abu Mohamed al-Jolani promised defeat for Hizbullah, which has significantly bolstered the Bashar Assad regime, in the mountainous border region between Syria and Lebanon.

The United States now launches a new investigation into suspected Islamic State group sympathizers almost every day, a senior official said Wednesday, underscoring the increased threat posed by the jihadist group.

Pointing to a significant uptick in cases linked to militants who now control swaths of territory in Iraq and Syria, the official warned Congress of "brinkmanship" over intelligence gathering powers that put national security at risk at a sensitive time.

The Islamic State jihadist group executed at least 20 men in the ruins of Syria's Palmyra on Wednesday, accusing them of fighting for the government, a monitoring group said.

"IS executed 20 men by firing on them in front of a crowd gathered in Palmyra's Roman theater, after accusing them of fighting for the Syrian regime," Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, told AFP.

Syrian Foreign Minister Walid Muallem said Wednesday that Iran and Russia would never give up their support for his regime in the face of a four-year-old armed revolt.

"I assure you that the relationship between Syria, the Russian Federation, and the Islamic Republic of Iran is much deeper than some people think," Muallem said at a press conference with his visiting Armenian counterpart Edward Nalbandian.

Saudi Arabia announced on Wednesday that it has imposed sanctions on two prominent members of Hizbullah on charges of “carrying out terrorist acts throughout the Middle East,” reported the Saudi Press Agency according to a statement issued by the kingdom.

It identified them as Khalil Harb and Mohammed Qabalan.

The EU on Wednesday asked its member states to admit 40,000 asylum seekers from Syria and Eritrea landing in Italy and Greece, which have been overstretched by an influx of migrants.

The emergency proposal, which comes atop another one to resettle in member states some 20,000 refugees who are outside Europe, is in response to a surge in migrants making the dangerous crossing over the Mediterranean.

Kurdish forces have driven the Islamic State group from more than a dozen Assyrian Christian villages that the jihadists had captured in northeastern Syria, a monitor said Wednesday.

"Following a 10-day offensive, Kurdish fighters took control early this week of 14 Assyrian villages that IS had controlled since February," said Rami Abdel Rahman, director of the Syrian Observatory for Human Rights.

A group of jihadists affiliated to al-Nusra Front were killed Wednesday in an ambush conducted by Hizbullah in the outskirts of the northeastern border town of Arsal.

The group was allegedly spotted with surveillance drones that were overflying the outskirts of Arsal and Nahle, Hizbullah's mouthpiece al-Manar said.

Progressive Socialist Party leader MP Walid Jumblat has called for preserving internal stability as the Islamic State extremist group continued to make more gains inside Syria.

The western city of Palmyra, home to a set of historic Roman-era ruins, was captured by the IS last week.