JERUSALEM — For decades, international law has held that territory seized in war must be returned. But Prime Minister Benjamin Netanyahu of Israel asserted Tuesday that this was no longer a given.

He made the argument after President Trump recognized Israel’s sovereignty over the Golan Heights, but his remarks, two weeks before a tight Israeli election, were taken to refer to the West Bank as well.

“There is a very important principle in international life,” Mr. Netanyahu said late Monday after attending the Golan signing ceremony at the White House. “When you start wars of aggression, you lose territory, do not come and claim it afterwards. It belongs to us.”

And moments before landing at Ben-Gurion Airport on Tuesday, he emphasized the point, telling reporters, “Everyone says you can’t hold an occupied territory, but this proves you can. If occupied in a defensive war, then it’s ours.”