Saudi Crown Prince Mohammed bin Salman has denounced Iran's supreme leader Ayatollah Ali Khamenei as the "new Hitler of the Middle East", as tensions simmer between the regional rivals.

Russia's military plans to reduce its involvement in Syria this year as it is nearing the completion of its goals there, the General Staff chief told journalists Thursday.

Syria's disparate opposition groups announced an agreement early Friday to send a united delegation to next week's UN-brokered peace talks in Geneva, as international diplomatic efforts intensify to end the six-year conflict.

The Kremlin said Thursday Turkey's opposition to the participation of Kurdish militias in Syria's political process would not stand in the way of a peace "congress" Moscow is seeking to organize in the near future.

"We know that there are certain reservations on the part of our Turkish partners with regards to the forces they believe pose a threat to their national security," Peskov told reporters at the Black Sea resort of Sochi.

Prime Minister Benjamin Netanyahu on Thursday rapped his deputy foreign minister for "offensive" remarks in which she said US Jews were too "comfortable" to understand threats to Israel.

Egypt's Prime Minister Sharif Ismail left the country Thursday for a three-week course of medical treatment and surgery in Germany amid speculation he would be permanently replaced in a cabinet shuffle.

Iraqi forces announced the launch of a major operation on Thursday to flush remaining Islamic State group fighters out of the western desert near the border with Syria.

After vetoing the renewal of a U.N.-led probe into chemical attacks in Syria, Russia on Wednesday said it was open to establishing a new panel to investigate the use of toxic gases in the six-year war.

Russian Ambassador Vassily Nebenzia told reporters that the "JIM is dead," referring to the Joint Investigative Mechanism (JIM) that shut down on Friday after two years of work to identify the perpetrators of chemical weapons attacks in Syria.

The government of war-ravaged Syria on Wednesday welcomed a deal between the presidents of its allies Russia, Iran and rebel backer Turkey to hold a peace "congress" of regime and opposition forces.

The Saudi-led coalition fighting in Yemen said Wednesday it would reopen a key Red Sea port and Sanaa airport to aid, after a more than two-week blockade following a missile attack on Riyadh.