Israeli military forces say they are preparing to launch a new offensive into the northern Gaza Strip, opening a second front in the operation aimed at freeing a kidnapped soldier.

In the past day, Israeli troops and armor moved into southern Gaza as airstrikes destroyed bridges and power plants. No casualties have been reported, but hundreds of thousands of Gazans are without power.

Palestinian officials denounced the offensive, calling it "collective punishment" for the recent kidnapping of three Israeli citizens. 

Israel says the Gaza offensive is a rescue operation.

Israel blames an exiled Hamas leader Khaled Mashaal living in Syria for ordering the soldier's kidnapping.

Four Israeli warplanes flew over Syrian President Bashar Assad's home early Wednesday to pressure him to work for the release of the soldier. Syria called the flyover an aggressive act and said its air defenses fired on the planes.

As tensions over the hostage-taking built, the Hamas-led Palestinian government proposed a prisoner swap to resolve the situation. Israel has not publicly responded to the offer.

Some information for this report was provided by AFP, AP and Reuters.