Updated

Israel's military said Sunday it launched an airstrike on its border with Syria after spotting militants carrying a bomb in the Israeli-held Golan Heights.

The military said it carried out the strike after troops saw "a group of armed terrorists" approach the border with an explosive intended to target Israeli troops. It said that Israeli aircraft "targeted the squad, preventing the attack."

It did not offer any casualty figure for the strike. The Britain-based Syrian Observatory for Human Rights said four Syrian soldiers were killed by a missile fired from Israeli-occupied territory in the Golan. Observatory director Rami Abdurrahman said it was not clear whether the missile was fired by a plane or from a vehicle.

On Twitter, Israeli Prime Minister Benjamin Netanyahu sent messages commending the soldiers involved in the strike.

"Any attempt to harm our soldiers and civilians will be met with a determined response like the military action tonight that thwarted a terror attack," Netanyahu said.

No one immediately claimed responsibility of the attack launched from inside Syria, which has been in the grips of a civil war since 2011. Syrian state media did not immediately report on the strike.

Israel has tried to stay out of the war in Syria, but it has spilled into the country before. In September, the Israeli military shot down a Syrian fighter jet in airspace over the Golan Heights, which Israel captured from Syria in the 1967 Middle East war and later annexed in a move that has never been internationally recognized. In August, Israel shot down a drone that came into the same airspace from Syria.

Israeli troops also have responded to occasional mortar fire from Syria. Israel says some of the attacks may have been accidental spillover, while others have been intentionally aimed at Israeli civilians and soldiers. It has always held Syria responsible for any cross-border fire.

Israel and Syria are bitter enemies. While relations are hostile, the ruling Assad family in Syria has kept the border area with Israel quiet for most of the past 40 years. Israel is concerned that the possible ouster of embattled President Bashir Assad's ouster could push the country into the hands of Islamic State extremists or al-Qaida linked militants, or plunge the region further into sectarian warfare.

It also repeatedly has threatened to take military action to prevent Syria from transferring advanced weapons to its ally, Hezbollah. Israel is believed to have carried out several airstrikes in Syria in recent years that have targeted sophisticated weapons systems, including Russian-made anti-aircraft missiles and Iranian-made missiles.

There were reports in Arab media last week that Israel had carried out another attack on such weapons in Syria. Israeli officials have not commented.

But just hours before the border strike Sunday night, Israeli Defense Minister Moshe Yaalon warned Syria and Iran against arming Hezbollah with such weapons.

"We will not allow the transfer of quality weapons to terror groups led by Hezbollah and we know how to reach them and those that dispatch them at any time," Yaalon said. He added that Iran is continuously trying to find ways to arm Hezbollah with the weapons.