Story highlights Sources say a strike mostly likely occurred in the Thursday-Friday time frame

The U.S. does not believe Israeli warplanes entered Syrian airspace

The United States believes Israel has conducted an airstrike into Syria, two U.S. officials first told CNN.

U.S. and Western intelligence agencies are reviewing classified data showing Israel most likely conducted a strike in the Thursday-Friday time frame, according to both officials. This is the same time frame that the U.S. collected additional data showing Israel was flying a high number of warplanes over Lebanon.

One official said the United States had limited information so far and could not yet confirm those are the specific warplanes that conducted a strike. Based on initial indications, the U.S. does not believe Israeli warplanes entered Syrian airspace to conduct the strikes.

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Both officials said there is no reason to believe Israel struck at a chemical weapons storage facilities. The Israelis have long said they would strike at any targets that prove to be the transfer of any kinds of weapons to Hezbollah or other terrorist groups, as well as at any effort to smuggle Syrian weapons into Lebanon that could threaten Israel.

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The Lebanese army website listed 16 flights by Israeli warplanes penetrating Lebanon's airspace from Thursday evening through Friday afternoon local time.

The Israeli military had no comment. But a source in the Israeli defense establishment told CNN's Sara Sidner, "We will do whatever is necessary to stop the transfer of weapons from Syria to terrorist organizations. We have done it in the past and we will do it if necessary the future."