The United States believes Israel has conducted an airstrike into Syria, CNN reported on Friday, citing two unnamed U.S. officials.

CNN quoted the officials as saying Israel most likely conducted the strike "in the Thursday-Friday time frame" and that Israel's warplanes did not enter Syrian air space.

It said the officials did not believe Israel had targeted a chemical weapons facility.

One U.S. official told the Associated Press that the strike appeared to hit a warehouse.

According to NBC News, which said it has confirmed the report with its own sources, it is believed the primary target was a shipment of weapons headed for Hezbollah in Lebanon. A senior U.S. official told NBC the airstrike was believed to be related to delivery systems for chemical weapons.

Syria's envoy to the United Nations said on Friday he was not aware of any attack by Israel against his country.

A White House spokeswoman referred questions on the reports to the Israeli government.

The Israel Defense Forces had no comment on the officials' remarks, but a source in the Israeli defense establishment told CNN: "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."

The CNN report said that during the time frame of the attack, the United States had collected information showing Israel Air Force planes flying over Lebanon.

Earlier Friday, sources in Lebanon reported that IAF jets conducted several sorties into Lebanese air space. Lebanese President Michel Suleiman called on the United Nations and the international community to press Israel to stop breaching Lebanon's sovereignty, saying that such flyovers are a " continuation of Israel's policy of aggression."

Israel has made clear in the past that it might intervene to prevent Syrian advanced weapons falling into the hands of militant groups, including Lebanon's Hezbollah, which fought a 34-day war with Israel in 2006.

In January this year, Israel reportedly bombed a convoy in Syria, apparently hitting weapons destined for Hezbollah, according to diplomats, Syrian rebels and security sources in the region.