Massively retaliating for what it said was an Iranian military strike across the Golan Heights, Israeli forces unleashed a heavy bombardment against Iranian military positions across Syria on Thursday, in a significant escalation that has brought the two long-hostile Middle East heavyweights to the brink of open war. The U.S. and a number of European powers quickly endorsed what they said was Israel’s right to self-defense, while the Russian government and U.N. Secretary-General Antonio Guterres urged both sides to pull back. But Israeli President Benjamin Netanyahu and his aides vowed to strike back hard at what they say are increasing encroachments by Iran and its proxies across the border in Syria. Israeli Defense Minister Avigdor Lieberman told reporters here that the Israeli missile and airstrikes had hit “nearly all” of Iran’s significant infrastructure sites in Syria. Iran and Tehran-allied militias have been active in Syria supporting the government of ally President Bashar Assad in the country’s seven-year civil war. The heavy Israeli strikes were in response to approximately 20 missiles fired from inside Syria at Israeli targets in the Golan Heights. “If it rains on us it will be a flood on them,” Mr. Lieberman said. Israeli Prime Minister Benjamin Netanyahu said Israel’s military action was intended to send a “clear message” to Tehran to back down, and hinted there may be more to come. Israel is in “a continuous campaign,” the conservative prime minister said, adding, “Whoever attacks us, we will attack them sevenfold, and whoever prepares to attack us, we will act against them first.” Already reeling from President Trump’s decision Tuesday to withdraw from the 2015 nuclear accord, Iranian leaders maintained a studied silence in the official media, seen by many as a sign Tehran realizes it is not ready for a direct, open conflict with the powerful Israeli military. A Foreign Ministry spokesman condemned what he called a “violation of Syria’s sovereignty,” without mentioning whether any Iranian forces had been hit in the attacks. The Syrian military acknowledged that the strikes destroyed a radar station and an ammunition warehouse, and damaged a number of air defense units. It said three people were killed and two were wounded, according to The Associated Press. The Britain-based Syrian Observatory for Human Rights, which closely monitors the civil war through sources inside Syria, said 23 fighters, including five Syrian soldiers, were killed..