The cross-border attacks, which were triggered by a botched Israeli undercover raid into Hamas-ruled Gaza late Sunday, marked the most serious escalation since an Israeli aggression in 2014.
International mediators appealed for restraint, hoping to avert another war.
The Israeli military said some 400 rockets and mortars have been launched from Gaza since the current round began on Monday afternoon, with about 100 of them intercepted by Israel's Iron Dome defense system, AP reported.
Israel has hit more than 100 targets it says are linked to militants in Gaza, including a strike that destroyed the TV station of Hamas.
On Tuesday, Gaza's health ministry said two Palestinians in their 20s were killed in separate airstrikes, raising the number killed since the Israeli offensive began Monday to six, including four militants. At least 25 people have been wounded.