The Israel Defence Forces (IDF) have carried out air strikes over Gaza City, killing at least four Hamas militants and injuring several other people.
It comes after a night of rocket fire from Gaza into southern Israel which injured at least three people.
Two large explosions were also heard in Gaza on Wednesday morning.
On Tuesday, an Israeli soldier was seriously injured by a bomb blast near the Gaza border fence. The previous day two militants died in an air strike.
One of the militants was a member of Hamas, the Islamist movement which governs Gaza. The other was from the Popular Resistance Committees (PRC).
The IDF said more than 50 rockets and mortar had been fired into Israel overnight, hitting at least one house. A number of the missiles were intercepted by Israel's Iron Dome missile defence system.
Israeli media said the three injured people were foreign workers.
Israel said three of the militants killed overnight were hit as they prepared to fire rockets. A fourth, a member of Hamas's military wing, was killed on Wednesday morning.
Hamas has in the past tried to rein in rocket fire from other militants groups, but was involved in the latest firing, along with the PRC.
The BBC's Jon Donnison in Gaza City says Hamas is under public pressure to be seen to be resisting Israel, especially if its members or civilians are killed.
Schools on either side of the border have been closed amid fears of further armed exchanges.
The violence comes only a day after the emir of Qatar became the first foreign head of state to visit Gaza since Hamas took power in 2007.
Our correspondent says neither Hamas nor Israel are thought to want a major escalation of conflict.
Following previous rounds of violence it has been the Egyptian government that has intervened to try and mediate a truce, he adds, but such ceasefires though do not usually hold for long.