Palestinian group Islamic Jihad has said one of its commanders was killed in an Israeli strike on his home in the besieged Gaza Strip.
The group's armed wing announced the death in a statement on Tuesday after Israel confirmed it had targeted Bahaa Abu al-Atta, 42, in a strike.
Islamic Jihad said al-Atta's wife was also killed in the blast that ripped through the building in Gaza City's Shejaiya district before dawn. At least two others were wounded, according to medics.
Islamic Jihad said al-Atta was killed while in the midst of "a heroic action", without elaborating, and promised to take revenge.
"Our inevitable retaliation will rock the Zionist entity," it said, referring to Israel, adding that it was on "maximum alert".
Hamas, the Palestinian group that administers the Gaza Strip, said that Israel "bears full responsibility for all consequences of this escalation" and promised that al-Atta's death "will not go unpunished".
The Israeli military said Prime Minister Benjamin Netanyahu had authorised the operation against al-Atta, blaming him for recent rocket, drone and sniper attacks against Israel, and attempted infiltrations into the country.
"Abu Al-Atta was responsible for most of the Palestinian Islamic Jihad's activity in the Gaza Strip and was a ticking bomb," it said, accusing Al-Atta of planning "imminent terror attacks through various means".
Al Jazeera's Harry Fawcett, reporting from West Jerusalem, said the killing of al-Atta marked "an extremely dangerous escalation".
"Israel has not targeted leaders in this way for some time so this strike is seen here as one which brings significant risks."
Shortly after the attack, a salvo of rockets was launched into Israel, witnesses said. The Israeli military said that air raid sirens sounded across central and southern parts of the country.
There was no immediate word of casualties or damage on the other side. Israeli police said they closed some roads on the edge of Gaza as a precaution, while crossings between Israel and Gaza were also closed. Schools and some ministries in Gaza were also closed, Fawcett said.
Separately on Tuesday, Syrian state media said that Israel launched a missile attack targeting the home of an Islamic Jihad official in the Syrian capital, killing one of his sons.
State news agency SANA said at least two people were killed in the attack in Mezzah, a western district of the city, while six others were wounded.
Islamic Jihad said political leader Akram al-Ajouri survived the attack on his home and blamed the "Zionist criminal enemy".
There was no immediate comment from Israel.