GAZA, March 25 (Xinhua) -- Qassam Brigades, the armed wing of the Islamic Hamas Movement, staged on Sunday "defensive drills" in the Gaza Strip amid mounting tension with Israel.

Hundreds of Qassam militants, carrying light machine guns, were deployed on main streets across the Gaza Strip, which Hamas ruled since its violent takeover in 2007.

Explosions were heard in different parts of the coastal territory, while tank-like military vehicles were also observed.

Local sources reported that a number of missiles were also fired into the sea.

Observers believe that Hamas military exercises are aimed at testing the readiness and coordination of its land, naval and air forces.

This is the first time for Qassam Brigades, which embrace thousands of well-trained fighters, to launch defensive exercises in Gaza.

The drills come days after units of Israeli and U.S. armies wrapped up joint military maneuvers in Israel.

Hours before the exercises started, Israeli air raids targeted a Qassam military site in Southern Gaza Strip city of Rafah, causing grave damages, but no casualties.

The Israeli airstrikes came in response to an earlier infiltration of four Palestinians who crossed the border fence into Israeli territories and damaged an Israeli army machine.

The Israeli army held responsible for all anti-Israel hostile activities in Gaza, warning of urging Palestinians there to demonstrate along the border fence.

The army stressed that such demonstrations are used as a cover to target the security of Israel, its soldiers and citizens.

Meanwhile, spokesman for Hamas, Fawzi Barhoum, said in a press statement that the Israeli airstrikes aim at foiling the preparations for massive marches the Palestinians are preparing.

Hamas and other Palestinian factions are preparing for a large popular demonstration along the borders withe Israel that will be held on March 30 to protest the blockade that Israel has imposed on the Hamas-ruled enclave since 2007.

Hamas called on Gaza populations to peacefully demonstrate during the big march close to the borders with Israel.