The battle against the Islamic State group's extremism may last a generation, Australian Foreign Minister Julie Bishop has warned, likening the jihadists to fanatical followers of Adolf Hitler.

Bishop said the pernicious threat of global terrorism was one that "keeps me awake at night" and urged a strong counter-narrative to the messages of hate and division spread by violent extremists.

Syria's military shot down a U.S. drone over the coastal province of Latakia, a stronghold of President Bashar Assad, state media said on Tuesday.

The U.S. military confirmed that it had lost communication with an unarmed Predator drone over northwest Syria on Tuesday and was looking into the claims it was brought down.

A High Court judge on Tuesday barred a 16-year-old boy from leaving Britain amid concerns that he might follow his three brothers in joining al-Qaida-linked fighters in Syria.

In an extraordinary move, Judge Anthony Hayden made the teenager a ward of court following a request by the boy's local authority, saying he wanted to "keep this lad alive."

The Turkish authorities have detained a British woman in the capital Ankara on suspicion of planning to go to Syria to join jihadist fighters, a government official said on Tuesday.

The detention of the woman, aged 21, comes after Turkey last week arrested three British male teenagers suspected of trying to travel to Syria.

Five Syrian migrants were found dead on Tuesday after their boat sank en route from Turkey to EU waters, the latest tragedy off the Turkish coast, reports said.

Eight migrants were rescued from the boat, which was carrying 15 people from Syria and Iraq, the official Anatolia news agency said, with rescue efforts continuing to find the remaining missing.

Turkish Prime Minister Ahmet Davutoglu on Tuesday rubbished suggestions that talks should be held with President Bashar Assad, saying negotiating with the Syrian leader was no different to shaking hands with Nazi tyrant Adolf Hitler.

U.S. Secretary of State John Kerry said in a weekend interview that Washington would have to talk with Assad eventually if peace was to be forged, in comments that drew a strong rebuke from Ankara which said there was nothing to negotiate with Assad.

U.N. investigators offered Tuesday to share information from secret lists of alleged Syria war criminals with prosecutors, to help bring perpetrators to justice.

The commission of inquiry on the human rights situation in Syria has been compiling lists of people suspected of committing war crimes in the brutal Syrian conflict for the past four years, but kept them secret for use in future prosecution.

The United States embassy in Saudi Arabia said it would remain closed to the public for a third day Tuesday because of "security concerns".

Consular services had initially been suspended on Sunday and Monday but the closure will continue for an extra day, a notice on the embassy website said.

Six people, including three young children, were killed in an alleged regime gas attack in northwestern Syria late Monday, a monitoring group and opposition activists said.

The attack prompted outrage from rights group Amnesty International, which said it was further evidence of regime "war crimes."

Fighters linked to the Islamic State of Iraq and the Levant (ISIL) in the Syrian al-Qalamoun are reportedly mobilizing and moving closer to the border with Lebanon ahead of a battle along the country's eastern border.

Lebanese and Syrian security sources said in comments published on Tuesday in al-Akhbar newspaper that ISIL fighters are moving “from eastern al-Qalamoun to its west” in preparation for a battle in the area in the spring after the snow melts.