Ministers from 47 European nations agreed for the first time Tuesday to harmonize their laws to stop so-called foreign fighters travelling to Iraq and Syria to join jihadist groups.

The agreement by the Council of Europe, a pan-European rights group which includes the EU but also takes in countries such as Russia and Turkey, will make cross-border tracking and prosecutions easier.

Air strikes by a U.S.-led coalition against the Islamic State group in northeastern Syria have killed around 170 jihadists in the past 48 hours, a monitoring group said Tuesday.

"The jihadists were killed in the past 48 hours in the province of Hasakeh, nearly all of them in very intense air strikes by the international coalition which is helping Kurdish forces in the area," said the Syrian Observatory for Human Rights.

Syria's President Bashar Assad on Tuesday praised Iran's support as a "key pillar" in his fight against rebels, as a third Iranian official visited Damascus in less than a week.

The visits come after several military losses for the Syrian government and as Tehran negotiates a key nuclear deal with the United States, which backs the rebels fighting Assad.

A rebel coalition including Al-Qaida's local affiliate seized the Syrian regime's largest remaining military base in northwest Idlib province on Tuesday, after an explosion and heavy clashes, a monitor said.

"All regime forces have withdrawn from Al-Mastumah, the largest regime base in Idlib, leaving it completely in the hands of opposition fighters," Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, told AFP.

Islamic State group jihadists attacked a village in Syria's southern Druze heartland on Tuesday and clashed with pro-government forces north of the ancient city of Palmyra, a monitoring group said.

"IS killed five fighters from the National Defense Forces and one woman in their attack on the Druze village of al-Haqef in Sweida province," said Syrian Observatory for Human Rights director Rami Abdel Rahman.

The mother of Austin Tice, a freelance reporter who went missing in Syria more than 1,000 days ago, made an emotional plea on Tuesday for his release.

Speaking in Beirut, Debra Tice urged anyone with information about the fate of her son to come forward, and asked his captors to consider allowing him to phone her or meet a friend of the family.

Hizbullah chief Sayyed Hassan Nasrallah has discussed with the adviser of Iran's supreme leader the latest security and political developments, Hizbullah announced on Tuesday.

Nasrallah likely met on Monday with Ali Akbar Velayati, who was in Beirut on a one-day official visit.

Jordan on Tuesday rejected Syrian accusations that "terrorists" were being given military training on its soil, insisting Amman favored a political solution to its neighbor’s conflict.

The Syrian foreign ministry, in a protest letter sent to the United Nations on Monday, alleged Jordan "provides logistical support to armed terrorist groups, including (al-Qaida affiliate) al-Nusra Front".

Mexican Foreign Minister Jose Antonio Meade, who is on an official visit to Beirut, said he is looking forward for a wider cooperation with Lebanon to help it confront the burden of Syrian refugees.

“Part of our dialogue with Lebanon should take into consideration Lebanon's burden in assisting the refugees,” Meade told An Nahar daily in an interview published on Tuesday.

Australia on Tuesday ruled out any leniency for returning jihadists following reports that three of its nationals suspected of fighting with Islamic State were in secret negotiations with Canberra to come home.

The Australian newspaper said the three had approached authorities via intermediaries or family members, but that the talks were stalled over what punishment they would face and fears of the risk they might pose if they were reissued passports and allowed to return.