As Israel marked the fiftieth anniversary of the Six Day War, Prime Minister Benjamin Netanyahu vowed Tuesday to “forever” maintain control of the Golan Heights, which was captured during that war.

He said the territory belonged to Israel and warned that any withdrawal would bring Islamist extremists onto the strategic plateau.

“The Golan Heights will forever remain under Israeli sovereignty. We will never leave the Golan Heights. It’s ours,” Netanyahu said at a conference of Israeli youth held outside the town of Katzrin on the Golan.

Israel captured the Golan from Syria. The West Bank, East Jerusalem, the Gaza Strip and the Sinai Peninsula were also taken by Israel during the conflict, which broke out after Egypt, Syria and Jordan mobilized to attack the Jewish state.

Israel never formally annexed the Golan, but in 1981 decided to apply Israeli law there, making it part of the country in every practical sense.

“If we are not here, radical Islam will be, and we all understand the consequences,” Netanyahu said.

Opposition leader Isaac Herzog, speaking at the same conference, echoed the prime minister’s words.

“At the 50-year anniversary of our victory in the Six Day War, we can say with certainty that the Golan is out of bounds [for negotiations] and an inseparable part of Israel,” he said.

Netanyahu made similar declarations in 2016, saying the Golan would remain “under Israel’s sovereignty permanently.”

Netanyahu said at the time that “the Golan was an integral part of the Land of Israel in ancient times. That is documented by dozens of ancient synagogues around us. And the Golan is an integral part of the State of Israel in the present time.”

The international community, including the US, Germany and the Arab League, rejected his assertions.

Before the outbreak of the Syrian civil war, the Golan Heights were seen as up for negotiations as part of a possible peace treaty with Syria.

However, that has become largely irrelevant in recent years. With no end to the Syrian conflict in sight, and the Syrian side of the Golan divided between various factions, there is nobody to talk to, even if Israel decided to open negotiations.

However, the Golan is likely to be key to any future peace deal with Syria, and its fate is an important part of a 2002 Saudi initiative that offered Israel peace with the Arab world in exchange for a full withdrawal from all territories captured in the 1967 war. While that offer is usually connected to areas sought by the Palestinians, the Golan is also considered occupied land by the international community.

AP contributed to this report.