Israel says it has shot down a Syrian warplane which entered its airspace - a rare incident between the two foes.
Two surface-to-air missiles were fired at the Sukhoi fighter jet, the Israel Defense Forces (IDF) tweeted.
According to Israeli reports, it happened over the Israeli-occupied Golan Heights. The pilot's fate is not clear.
Syrian news agency Sana said Israel had targeted the jet over Syrian airspace, but did not say whether it was hit.
Sana quoted an unnamed military source as saying the plane was conducting raids against "armed terrorist groups" near the southern Yarmouk Valley.
Syria routinely describes rebel groups as terrorists.
Israeli Prime Minister Benjamin Netanyahu later said that Syria had committed a "blatant violation" of a 1974 ceasefire agreement, which defines the lines of separation between the two sides' forces on the Golan Heights.
"We will not accept any intrusion... into our territory, either from the ground or from the air," Mr Netanyahu said, adding: "Our forces acted appropriately."
Israel's Haaretz news website said residents in northern Israel saw interceptor missiles fired and heard explosions.
Flames and smoke were also later seen rising from the area of the fence between Syria and the Israeli-occupied Syrian Golan Heights, AFP news agency reports.
By Tom Bateman, Middle East correspondent, Jerusalem
Today's trails of smoke above the Israeli-occupied Golan Heights are another sign of how Syria's war has agitated the dynamics between old foes in the region.
Israel and Syria fought their last war 45 years ago and later agreed to separate their forces either side of a 50-mile-long buffer zone - a boundary that had remained Israel's quietest since.
But with President Assad's men closing in on jihadist groups on the Syrian side of the zone - and pictured reportedly hundreds of metres from an Israeli observation post - Israel has been ratcheting up its rhetoric.
It is concerned most about the threat it sees from Syria's allies Iran and the Lebanese armed group Hezbollah, saying it will not tolerate any breach of the buffer zone deal.
But Syria will see the Sukhoi's downing as proof of its belief that Israel has been prepared to help rebel groups to stop the government's advances.
In a statement after the incident, the IDF said it was on "high alert" following "an increase in the internal fighting in Syria" and greater activity by Syria's air force in the region.
It said the fighter jet had infiltrated about 2km (1.25 miles) into Israeli airspace before it was intercepted by Patriot missiles.
An Israeli military spokesman said the plane had crashed "most likely in the southern part of the Syrian Golan Heights". About a third of the Golan Heights is still nominally controlled by Syria.
Israel considers the occupied Golan Heights, and the airspace above it, as Israeli sovereign territory, though this is not recognised internationally. It has occupied the area since the 1967 Middle East war.
It is reportedly the first time Israel has shot down a manned Syrian aircraft since 2014. Israel is not directly involved in the Syrian war but has attacked drones which have entered its airspace, and carried out dozens of air strikes on Syrian and Iranian military assets in Syria in recent years.
Tuesday's incident comes just a day after Israel deployed its David's Sling missile defence system - designed for use against medium-range missiles - for the first time.
The system was activated "in response to the threat" from two Syrian surface-to-surface missiles approaching Israeli territory, an army statement said.
Correction 26 July 2018: The headline of this article has been amended to more clearly reflect the IDF's statement regarding the incident.