On Saturday, Israeli officials confirmed that a day earlier, Israeli aircraft targeted advanced surface-to-surface missiles in Syria that were apparently bound for Hezbollah.
The missiles were believed to be m600s, a Syrian version of Iran's Fatah 110 missile, an extremely accurate guided missile capable of traveling roughly 300 kilometers (190 miles) with a half-ton warhead, an Israeli official said
The Israeli officials spoke anonymously because they had not been given permission to speak publicly about the matter.
In Washington, a Pentagon spokeswoman said she had no information relating to Sunday's report of a new Israeli airstrike in Syria.
President Barack Obama said Saturday, before the latest incident, that it was up to Israel to confirm or deny any strikes, but that the U.S. coordinates very closely with Israel.
"The Israelis, justifiably, have to guard against the transfer of advanced weaponry to terrorist organizations like Hezbollah," Obama told the Spanish-language TV station Telemundo.
Israel has said it wants to stay out of the brutal Syria war, but could inadvertently be drawn in as it tries to bolster its deterrence and prevent sophisticated weapons from reaching Hezbollah.
Since the conflict in Syria erupted more than two years ago, fighting has repeatedly spilled into Turkey, Lebanon, Iraq, Jordan and the Israeli-annexed Golan Heights.
Renewed concern about a wider conflagration come as Washington considers how to respond to indications that the Syrian regime may have used chemical weapons in its civil war.
Obama has described the use of such weapons as a "red line," and the administration is weighing its options — including possible military action.
Prime Minister Benjamin Netanyahu, meanwhile, has drawn his own red line, saying repeatedly that the Jewish state would be prepared to take military action to prevent Hezbollah from obtaining new weapons that could upset the balance of power.