Israeli air strikes killed seven Hamas members early yesterday, the Islamist group's armed wing said, making it their highest single death toll since a 2012 cross-border conflict.
Israeli military authorities confirmed the strikes, saying they "responded to rocket attacks against southern Israel", targeting known "terror" sites and concealed rocket launchers.
Hamas said the strikes were launched at a gathering point for its members in Gaza's southern-most town of Rafah, at the Egyptian border.
The group said six were killed in a single location, while a seventh died in a bombing shortly after midnight. It said that in all, nine Palestinian militants died in Israeli air strikes overnight.
Hamas' military wing said "the enemy will pay a tremendous price".
The Israeli attacks followed rocket strikes at Israel from Gaza, where Hamas is the dominant force. The Israeli military said there had been more than 150 since mid-June, including about 20 on Sunday alone.
Prime Minister Benjamin Netanyahu pledged to his cabinet on Sunday "to do whatever is necessary" to restore quiet to southern Israeli communities.
Netanyahu also cautioned against any rush toward wider confrontation with the group, whose arsenal includes long-range rockets that could reach Israel's business capital, Tel Aviv.
However, far-right members of Netanyahu's cabinet have pushed for a stronger response to the rocket fire that has disrupted life for many Israelis living in the southern region, where air raid sirens regularly send them running for shelter.
Yesterday's fatalities were the single largest toll for Hamas since Israel's campaign in late 2012 launched to halt rocket fire at its towns. In that eight-day campaign, 180 Palestinians and six Israelis were killed.