Israeli warplanes struck Sidon early Sunday, targeting a religious building run by a Shiite Muslim cleric close to Hezbollah in their first hit inside the southern port city, currently swollen with refugees from fighting further south.

Also early Sunday, a huge explosion reverberated across Beirut, apparently caused by an Israeli air raid on the capital's southern suburbs.

At least four people were wounded in the airstrike that targeted Sidon for the first time since Israel launched its massive military offensive against Lebanon and Hezbollah guerrillas July 12, hospital officials said.

CountryWatch: Israel

Click here for full Mideast coverage.

Strikes early in Israel's campaign hit bridges outside the city of 100,000, where 35,000 refugees are also now residing.

Witnesses said the Israeli jets fired two missiles that directly hit the four-story Sayyed al-Zahraa compound in Sidon. The compound, which contains a mosque, a religious library and a seminary, was entirely destroyed but was believed to be empty at the time of the strike, they said.

A man and his wife in a nearby house were lightly wounded from broken glass, while two other people strolling near the compound were also hit by shrapnel, a hospital official in Sidon said, speaking on condition of anonymity because he was not authorized to make statements to the media. The four were taken to hospital.

The compound is run by Sheik Afif Naboulsi, a Shiite Muslim cleric close to Iran and the militant Hezbollah group.

Minutes earlier, two other blasts also shook Beirut also caused by an Israeli airstrike on the southern suburbs where Hezbollah headquarters, including the residence of Hezbollah leader Sheik Hassan Nasrallah have been flattened by repeated Israeli bombing.

Israeli warplanes also hit targets in eastern Lebanon's Bekaa Valley firing missiles in the cities of Hermel and Baalbek at around 11 p.m. Saturday, witnesses said. There was no immediate word on casualties in either strike.