Prime Minister Benjamin Netanyahu defended the downing of a Syrian fighter jet that traveled into Israeli airspace on Tuesday afternoon, warning that Israel would continue to take similar action against any incursion into its territory.

Israel on Tuesday said the Sukhoi-model jet had traveled two kilometers into its airspace when it fired two Patriot missiles at the plane, shooting it down. The plane reportedly crashed inside Syria, killing its pilot. The fate of a second crewman was initially said to be unknown; later reports indicated there may only have been one pilot.

“Our air defense systems identified a Syrian air force plane taking off from the Syrian T-4 airbase and penetrating into Israeli airspace,” Netanyahu said in a statement. “This was a blatant violation of the 1974 separation agreement between us and the Syrians. We will not accept any such penetration of, or spillover into, our territory, neither on the ground nor in the air.”

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According to the IDF, the fighter jet took off from the Iran-linked T-4 air force base in central Syria, which Israel has bombed in the past, and traveled “at high speed” toward the Golan Heights.

“Our forces acted appropriately,” Netanyahu stressed in a tweet. “We insist that the Syrians strictly abide by the Separation of Forces Agreement between us and them.”

The IDF said it had noticed increased air force activity in southwestern Syria, near the border, since the morning. Syria and Russia have been waging a large air campaign to oust the last remaining pockets of rebels from the border region.

Syria claimed the jet had been in Syrian airspace when it was shot down.

IDF spokesman Jonathan Conricus said there was no “confusion” about the fact that this was a Syrian fighter jet. In the past, Israel has hesitated in shooting down incoming aircraft out of concerns they might belong to Russia.

Speaking at the UN Security Council meeting discussing the Middle East, Israel’s ambassador to the UN Danny Danon warned the country would take similar action on any border.

“Israel will not tolerate any violation of our sovereignty – not from Syria, not from Gaza, not from any other enemy that threatens our security,” he said.

The 1974 Separation of Forces Agreement requires Syria to abide by a demilitarized zone between the two countries.

The agreement was drawn up in the wake of the 1973 Yom Kippur War established a demilitarized zone between Israel and Syria.

Tuesday’s breach of Israeli airspace, and the interception, set off incoming rocket alert sirens throughout northeastern Israel, sending thousands of residents rushing to bomb shelters for the second day in a row.

On Monday, Israel’s David’s Sling missile defense system attempted to intercept two missiles shot as part of internal fighting in Syria, in an apparent false alarm.

Construction Minister Yoav Galant (Kulanu), a former IDF commander of the Southern Command, said shooting down the jet sent a message to Iran, Syria, and Hezbollah.

“Violating Israel’s airspace crosses the red line,” he said.

Judah Ari Gross contributed to this report.