Palestinian armed groups staged military exercises in Gaza on Tuesday, including firing rockets into the sea, to mark the anniversary of the start of the 2008 conflict with Israel.

The demonstrations were scheduled to last several hours and involve about 10 groups in the Israeli-blockaded Palestinian enclave, said a spokesman for the Al-Quds Brigade forces, the armed wing of Islamic Jihad.

The goal of the exercise, the first of its kind, is to "strengthen the skills of combatants" and demonstrate the "unity" of armed groups in Gaza, added the spokesman, whose face was almost entirely covered by a traditional headscarf.

Hamas, the Islamist group that has controlled Gaza since 2007, was also taking part. Hamas's Al-Aqsa TV showed rockets being fired from the strip on Tuesday into the Mediterranean Sea.

Israel's army said a projectile device was launched from Gaza overnight Monday to Tuesday, but that it did not cross into Israeli territory.

Israel did not immediatly retaliate to that launch with airstrikes, as it typically does when rockets fired from Gaza enter Israel. 

The drills also come days after Hamas accused Israel of launching strikes that damaged a children's hospital.

Israel, which said it carried out the weekend airstrikes in response to rocket fire from Gaza, denied that its missiles hit the hospital.

In December 2008, Israel launched "Operation Cast Lead" to stop Palestinian rocket fire into Israel.

It ended with a ceasefire in January 2009, after 1,440 Palestinians and 13 Israelis were killed.

Hamas and Israel fought two further conflicts, in 2012 and 2014. 

A fragile truce has broadly held in recent months, despite rocket fire from Gaza which is generally followed by retaliatory Israeli air strikes.

Poverty rates in Gaza, which hovered around 50 percent before the coronavirus pandemic, are thought to have increased since Hamas imposed lockdown measures to limit transmission.