At least eight Palestinians, including children, have been killed in mortar attacks and airstrikes in the Gaza Strip.
The deaths occurred in two separate attacks on the eastern part of Gaza City on Tuesday, witnesses said.
Two of the dead were aged 11 and 16, and four of them were from the al-Quds Brigade, the armed wing of the Islamic Jihad movement, a spokesman for the group said.
Four people died when a shell slammed into a family home in Shejaiya, medical sources told AFP news agency. Several hours later, another four were killed - all of them fighters - in an air raid in the nearby Zeitun neighbourhood.
On Tuesday, the military said it was responding to rocket attacks from Gaza. It also confirmed it had fired mortar rounds towards the eastern outskirts of Gaza City on Tuesday, shortly after four rockets hit Israel, and expressed "regret" over reports that civilians had been hurt.
It was the third time Shejaiya had been targeted on Tuesday, following an earlier one which wounded one fighter and a burst of tank fire, which left two civilians wounded shortly after dawn.
Al Jazeera's Bernard Smith, reporting from Gaza, said that more tit-for-tat attacks could be expected.
"Tensions look to be rising here, and violence could increase," he said.
The latest incident also comes after at least 19 people were wounded in a series of raids on Monday, in the northern town of Beit Lahiya and Gaza City.
Witnesses said a security compound for Hamas, which controls the Gaza Strip, a training camp north of the city and a brickworks and metal foundry in northern Gaza were among the targets.
Rising cross-border violence has occurred, also increasing tensions between Israel and Hamas and once again raising fears of another large-scale Israeli invasion.