Syrian President Bashar Assad told Russia he ordered his army to deploy rocket batteries aimed at Israel in response to airstrikes on Damascus, aides said.
The aides were quoted in a report Monday by the Almiadin television station in Lebanon.
Assad asked Russia to convey a message to Washington that if Israel attacks Syrian sovereign territory he will view the acts as a declaration of war, Israel Radio said.
In a chain of explosions that rocked Damascus before dawn Sunday, at least 100 Syrian soldiers were killed, an unnamed Syrian doctor at the military's Tishreen Hospital said in a report in The New York Times.
Assad said he would allow Palestinian organizations operating in his country to wage attacks against Israel from the Golan Heights, Syrian state television reported.
The Israeli army raised its level of alert along its northern border with Syria, Israel Radio said.
Haaretz reported the number of civilians frequenting gas-mask distribution centers in Israel has quadrupled in recent days.
Israel will continue to maintain silence about the airstrikes, Haaretz said.
An unnamed senior Israeli official said the goal is to convey to Assad that Israel's sole interest is to prevent advanced weaponry from reaching the Lebanese miliant group Hezbollah. Israel does not want to intervene in Syria's civil war or help rebels topple his regime, Haaretz said.
The airstrikes were aimed at destroying advanced Iranian-made Fatah 110 missiles said to be en route to Hezbollah, reports said.
Two Iron Dome missile defense batteries were positioned near Israel's northern border in response to "ongoing situational assessments," an Israeli military spokesman said.
Arkia Israeli Airlines, Israel's second-largest airline, said its flights in the northern district were canceled on military orders until Thursday.
"The Israeli aggression opens the door to all possibilities and confirms the organic correlation between expiatory terrorist groups and the Israeli enemy," Syrian Information Minister Omran Zoubi said in a report carried by the state news agency SANA, monitored by United Press International.
Syrian Deputy Foreign Minister Faisal al-Mekdad said the attacks amounted to a formal act by which one nation goes to war against another.
"When they attack, this is a declaration of war," he told CNN. "This is not something that is [new]," al-Mekdad said. "We dealt with this on several occasions, and we retaliated the way we wanted, and the retaliation was always painful to Israel, and they will suffer again."
The actions and rhetoric followed a second set of powerful explosions deep inside Syria early Sunday that Syria said came from Israeli missile attacks on a Syrian military installation -- the second set of airstrikes by Israel in three days.
Israeli Prime Minister Binyamin Netanyahu made no mention of the raids at a public appearance Sunday, but spoke pointedly about a commitment to keeping Israel secure.
"[My father] taught me that the greatest responsibility we have is to ensure Israel's security and guarantee its future," he said, dedicating a highway interchange named after his father, Benzion Netanyahu, a historian who died a year ago.
U.S. officials privately said the Sunday attacks were aimed at surface-to-surface missiles bound for the Lebanese militant group Hezbollah from Iran.
The missiles were being stored in a warehouse at Damascus International Airport when they were struck, a U.S. official told The New York Times.
Syrian officials said Israel attacked a military complex at Jamraya just outside Damascus.
In late January, Israel carried out a similar airstrike in Syria, which it also refused to publicly confirm, that used similar tactics, including a route over Lebanon, U.S. officials said.
U.S. and European diplomats told The Wall Street Journal Israeli officials had privately told U.S. and European counterparts Israel would take action if needed to stop advanced rockets from reaching Hezbollah.
The White House Sunday reiterated a position President Obama stated Saturday that Israel had a right to defend itself.
"The Israelis are justifiably concerned about the threat posed by Hezbollah obtaining these advanced weapon systems," spokesman Josh Earnest told reporters. He said Obama believed Israel, "as a sovereign government, has the right to take the actions they feel are necessary to protect their people."
U.N. Secretary-General Ban Ki-moon warned against escalating the situation into a regional conflict.
"The secretary-general calls on all sides to exercise maximum calm and restraint, and to act with a sense of responsibility to prevent an escalation of what is already a devastating and highly dangerous conflict," a Ban spokesman said.