US Defense Secretary Jim Mattis said during a visit to Israel on Friday there can be "no doubt" Syria has retained some chemical weapons and warned President Bashar al-Assad's regime not to use them.

Mattis made the comments as he began a one-day visit for talks with Israeli leaders, who strongly supported the recent US strike against an airbase in neighbouring Syria over an alleged chemical attack on a rebel-held town.

Hundreds of frightened Syrian evacuees were on the move again Friday after being blocked for 48 hours at a transit point where a bomber killed dozens of their fellow townspeople, a monitor said.

Ten of the 45 buses carrying civilians and loyalist fighters from the besieged government-held towns of Fuaa and Kafraya left the marshalling area in rebel-held Rashidin, the Syrian Observatory for Human Rights said.

The U.N.'s Syria envoy said Thursday that he will hold talks with Russian officials next week but without the U.S. present after previous plans for a trilateral meeting were "postponed."

The Egyptian military said Thursday it killed a senior Islamic State group cleric and 18 jihadists in air strikes in the Sinai Peninsula where the extremists are waging an insurgency.

An Israeli court on Thursday extended the remand of an Israeli-American teenager accused of making dozens of anti-Semitic bomb threats in the United States and elsewhere, police said.

Several dozen Palestinian protesters clashed with Israeli forces Thursday outside a prison where detainees are on a hunger strike, while a group of Israeli hardliners nearby taunted prisoners by barbecuing.

Syria still has up to three tons of chemical weapons, Israeli defense officials said Wednesday in the first specific intelligence assessment of President Bashar Assad's weapons capabilities since a deadly chemical attack earlier this month.

The estimate came as the head of the international chemical weapons watchdog said laboratory tests had provided "incontrovertible" evidence that victims and survivors of the April 4 attack in northern Syria were exposed to sarin nerve gas or a similar banned toxin.

The global chemical arms watchdog Thursday "overwhelmingly" rejected a Russian-Iranian move to launch a new investigation into a suspected chemical attack in Syria, delegates said, backing the probe already underway.

US Secretary of Defense Jim Mattis arrived in Cairo Thursday on the latest leg of a regional tour, as ties with Egypt continue to warm under President Donald Trump.

After touching down at Cairo airport, Mattis set off to meet President Abdel Fattah al-Sisi, who was hailed by Trump during a White House visit earlier this month.

Hundreds of frightened Syrian evacuees from two besieged government-held towns were stuck at a rebel-held transit point on Thursday where dozens of their fellow townspeople were killed in a weekend bombing.