BEIRUT/JERUSALEM (Reuters) - Reports of an explosion at a Syrian military base late on Wednesday have prompted speculation of a new Israeli attack on Syria but Israeli officials would not confirm a report on CNN that their jets had carried out a strike.

The channel quoted an unidentified U.S. official on Thursday as saying Israeli warplanes struck a Syrian base near the port of Latakia. But Israeli officials declined comment.

"We're not commenting on these reports," a spokesman for the Israeli Defence Ministry said.

One Israeli official, speaking on condition of anonymity, said he thought that Israel had indeed carried out a strike. He stressed that he was not entirely certain, however.

Israel has repeatedly warned that it is prepared to use force to prevent advanced weapons, notably from Iran, reaching Lebanon's powerful Shi'ite Muslim guerrillas through Syria. It carried out several air strikes on Syria earlier this year.

The Syrian Observatory for Human Rights, which collates reports from opposition activists, said late on Wednesday that there had been an explosion at Syrian air defence base near Jableh, in the Mediterranean coastal province of Latakia.

The Lebanese military said six Israeli jets flew over Lebanese territory on Wednesday. Israeli aerial incursions over Lebanon are frequent, but such high numbers have in the past sometimes been an indication of military strikes against Syria.

(Writing by Alastair Macdonald; Editing by Mark Heinrich)