Syrian state media said Israeli strikes hit the Tartus area on Monday, after a war monitor reported a blast near the city's port and the Israeli army said it struck a "military site" further north.

That came after Israel carried out hundreds of air strikes after a lightning Islamist-led offensive ousted president Bashar al-Assad in December, in what it said was a bid to prevent Syrian military assets from falling into hostile hands.

It also sent troops into a UN-patrolled buffer zone that has separated Israeli and Syrian forces on the strategic Golan Heights since 1974.

UN envoy for Syria Geir Pedersen said Tuesday he was "deeply concerned by continued violations of the 1974 Disengagement of Forces Agreement".

Such actions, he warned in a statement, "are unacceptable and risk further destabilising an already fragile situation, heightening regional tensions, and undermining efforts toward de-escalation and a sustainable political transition."

Israeli Prime Minister Benjamin Netanyahu said last month that southern Syria must be completely demilitarised, warning that his government would not accept the presence of the forces of the new Syrian Islamist-led government near its territory.

Even before Assad's fall, during Syria's civil war which broke out in 2011, Israel carried out hundreds of strikes in the neighbouring country, mainly on government forces and Iranian-linked targets.

The same day Assad was ousted, Israel said its troops were entering the UN-patrolled buffer zone on the Golan Heights.

Israel seized much of the Golan Heights from Syria in a war in 1967, later annexing the area in a move largely unrecognised by the international community.

Pedersen's statement called on Israel "to cease violations, uphold its international obligations, and refrain from unilateral measures that exacerbate conflict."

It urged "all parties to respect Syria's sovereignty, unity, independence, and territorial integrity."

"Constructive dialogue and strict adherence to international agreements and international law are essential for security in Syria and the broader region."