Britain, France and Germany accused Iran on Tuesday of growing its stockpile of high enriched uranium to "unprecedented levels" without "any credible civilian justification."

The three countries known as the E3 said in a statement ahead of a UN Security Council meeting Tuesday on Tehran's nuclear program that Iran must "reverse its nuclear escalation."

Iran has increased its manufacturing of enriched uranium such that it is the only non-nuclear weapons state to possess uranium enriched to 60 percent, the International Atomic Energy Agency (IAEA) nuclear watchdog said.

Bashar al-Assad's overthrow has cleared the way for US strikes against the Islamic State group in areas previously shielded by Syrian and Russian air defenses -- but the jihadists may also try to exploit the vacuum left by his fall.

The militant group,often referred to as ISIS or IS, rose out of the chaos of the Syrian civil war to seize swathes of territory there and in neighboring Iraq, prompting a US-led air campaign starting in 2014 in support of local ground forces who ultimately defeated the jihadists.

Britain, France and Germany accused Iran on Tuesday of growing its stockpile of high enriched uranium to "unprecedented levels" without "any credible civilian justification."

The three countries known as the E3 said in a statement ahead of a UN Security Council meeting on Tehran's nuclear program that Iran must "reverse its nuclear escalation."

Iran has increased its manufacturing of enriched uranium such that it is the only non-nuclear weapons state to possess uranium enriched to 60 percent, the International Atomic Energy Agency (IAEA) nuclear watchdog said.

The leader of the Kurdish-led Syrian Democratic Forces on Tuesday proposed a "demilitarised zone" in the northern town of Kobane as fighting with Turkish-backed groups grips northern Syria.

"Reaffirming our firm commitment to achieving a comprehensive ceasefire across all of Syria, we announce our readiness to propose the establishment of a demilitarised zone in the city of Kobane, with the redeployment of security forces under American supervision and presence," Mazloum Abdi wrote on X.

International Organization for Migration chief Amy Pope said Tuesday the UN agency was not advising the large-scale return of refugees to Syria before the situation has stabilised after the ouster of Bashar al-Assad.

"People have the right to return home... but we are not advising any sort of large-scale return... the system can't bear that kind of influx," Pope said.

The military chief of Syria's victorious Islamist group Hayat Tahrir al-Sham said on Tuesday it would be "the first" to dissolve its armed wing and integrate into the armed forces.

"In any state, all military units must be integrated into this institution," Murhaf Abu Qasra, known by his nom de guerre Abu Hassan al-Hamawi, said in an interview with AFP, adding that "we will be, God willing, among the first to take the initiative (to dissolve our armed wing)".

Syria's conflict has not ended even after the departure of Bashar al-Assad, the UN's envoy to the country warned Tuesday, as the Security Council called for an "inclusive" political transition.

Geir Pedersen, the UN's special envoy for Syria, also called at the Security Council for Israel to "cease all settlement activity in the occupied Syrian Golan" and said an end to sanctions would be key to assisting Syria.

Syria's "conflict has not ended yet," even after the departure of former president Bashar al-Assad, the UN's envoy to the country warned Tuesday, highlighting clashes between Turkish-backed and Kurdish groups in the north.

"There have been significant hostilities in the last two weeks, before a ceasefire was brokered... A five-day ceasefire has now expired and I am seriously concerned about reports of military escalation," said Geir Pedersen, the UN's special envoy for Syria.

"Such an escalation could be catastrophic."

Israeli Prime Minister Benjamin Netanyahu held a security briefing Tuesday atop a strategic Syrian mountain inside the UN-patrolled buffer zone on the Golan Heights that Israel seized this month, the defence minister said.

Netanyahu, Defence Minister Israel Katz and the heads of the armed forces and the domestic security agency visited "outposts at the summit of Mount Hermon for the first time since they were seized by the military", Katz's office said.

Iran's supreme leader said Tuesday that Israel and the United States were "completely wrong" to imagine the Tehran-backed axis of resistance had collapsed with the ouster of Syria's longtime strongman.

"With the developments in Syria and the crimes the Zionist regime is committing and the crimes that America is committing, and the help that some others are giving to them, they thought that the resistance was over," Ayatollah Ali Khamenei said in a televised speech.

"They are completely wrong."