Secretary-General Ban Ki-moon's office issued a statement Thursday expressing "grave concern" about the incident, but said U.N. officials lacked details about exactly what had happened.

CNN: Israeli defense minister suggests role in Syria airstrike

Annan himself expressed grave concerns about the situation in Syria in a letter to the U.N.

CNN: STORY HIGHLIGHTS

United Nations Secretary-General Ban Ki-moon expressed "grave concern" over the reports of Israeli airstrikes in Syria Sunday but stressed that the U.N. is not "in a position to independently verify what has occurred, " his spokesman said.

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