An Israeli airplane struck a Palestinian on his motorbike in central Gaza Strip Tuesday, wounding him seriously as Hamas militants fired a fresh barrage of rockets into Israel.

In a statement, Hamas, which controls Gaza, said its militants fired 10 Grad rockets into Israel "in response to the frequent crimes of the Zionist occupation."

Hamas has often refrained from participating in cross-border violence that has been taking place every now and then for more than a year. Islamic Jihad and smaller groups used to take part in the waves of violence while Hamas focused on calming down the situation.

The firing of the Grads came on the second day of tension that left six Palestinians killed in three separate Israeli military strikes in the Gaza Strip. This volley of rockets are likely to trigger a fiercer Israeli military response.

Earlier Tuesday, a Palestinian ambulance crew lifted bodies of two militants in eastern Gaza Strip.

The two were wounded in an Israeli military strike near the border fence to the east of central Gaza Strip. Israel allowed the ambulance to reach the area in the morning and the wounded were already dead, medical sources said.

On Monday, four Palestinians were killed, including two Islamic Jihad members, in two Israeli army strikes in northern Gaza Strip. The Islamic Jihad militants were observing a routine activity for Israeli tanks on the Gaza side of the border, while the other two dead were firing rockets into Israel.

The armed wing of Hamas, the Islamic movement that controls Gaza, announced its responsibility for firing four rockets into southern Israel. The declaration is the first in months, as Hamas committed almost fully to an unofficial ceasefire that took effect after the end of Israel's Operation Cast Lead against Gaza in January 2009.

Israel said two projectiles landed on its territories and caused no damage or casualties.

The escalation in Gaza coincided with the death of an Israeli worker in clashes between the army and militants who infiltrated into Israel from Sinai. The army said it still did not verify if the two assailants, who were gunned down, were linked to Gaza groups.