Syria

A senior U.S. official said that Tariq bin Tahar al-'Awni al-Harzi, a Tunisian, was killed by a U.S. drone strike and that there were no reports of any civilian casualties in the operation. It was not clear if anyone else was with al-Harzi or if other militants were killed or injured in the strike.

The official was not authorized to discuss the operation publicly so spoke on condition of anonymity.

Thursday's letter comes a week after more than 70 countries expressed "outrage" and demanded that the council prevent Syria's air force from using the weapons, which are prohibited by international humanitarian law because of their indiscriminate nature.

The council meets informally Friday to explore how the international community should respond as Syria's fighting is deep into a fifth year with well over 200,000 killed.

The council more than a year ago called for an end to the use of barrel bombs, but it has not followed up.

The two-pronged attack on the northeastern city of Hassakeh and the border town of Kobani came two days after an Islamic State spokesman acknowledged that the group might lose some battles but would not be defeated. 

The spokesman, Abu Muhammad al-Adnani, had urged militants to strike back at their foes during the Muslim holy month of Ramadan and "shake the ground beneath them."

The early morning assault by IS captured part of Hassakeh, which has long been divided between Syrian Kurds and the military forces of President Bashar Assad.

Maamoun Abdulkarim, the head of the government's Antiquities and Museums Department, told The Associated Press that the extremists destroyed the grave of Mohammad Bin Ali, a descendant of Imam Ali, cousin of Islam's Prophet Muhammad and a deeply revered Shiite saint.

The grave was just north of Palmyra.

The second tomb is close to the city's famed Roman-era archaeological site and was the final resting place of a Sufi scholar, Nizar Abu Bahaa Eddine, who lived in Palmyra some 500 years ago.

They are fleeing intense fighting in northern Syria between Kurdish fighters and jihadis.

The flow of refugees came as Syrian Kurdish fighters closed in on the outskirts of a strategic Islamic State-held town on the Turkish border, Kurdish officials and an activist group said, potentially cutting off a key supply line for the extremists' nearby de facto capital.