Syria's air defense system responded to a missile attack on the Shayrat airbase in the city of Homs early Tuesday morning Hezbollah and Syrian army sources reported, according to Lebanon's Daily Star. The missiles were intercepted and shot down, the report claims.Further unconfirmed Syrian military sources reported that military aircraft violated Syrian airspace. The Syrian military has tentatively identified the aircraft as Israeli planes, according to the source cited by Al-Masdar news.The Shayrat airbase was targeted by an American strike last year."There is no US military activity in that area at this time," Pentagon officials said, responding to the reports of the attack on the Homs airbase.