Tunisian President Beji Caid Essebsi has said U.S. surveillance drones are flying over the Tunisian-Libyan border to ward of attacks by Islamic State, after lawmakers called on his government to clarify U.S. reports on such a mission. In Tunisia, any U.S. military presence on its soil is a sensitive topic. Opponents say it would be a breach of sovereignty. Last month U.S. government sources said U.S. surveillance drones had begun flying into Libya from a Tunisian air base. But Essebsi, in a television interview broadcast late on Tuesday, said the measure was needed to avoid cross-border attacks by militants such as an Islamic State assault on the Tunisian town of Ben Guerdan in March. The drones being used were unarmed, Essebsi said, and in a repeat of previous denials, added there was no U.S. base in Tunisia.