A ball of fire is seen following an Israel airstrike at Khan Yunis in the southern Gaza Strip on Saturday. AFP
Israeli air force jets have struck Hamas positions in the Gaza Strip on Saturday.
The exchange came after Hamas warned that Israel's planned annexation of parts of the occupied West Bank amounted to a "declaration of war."
Security sources in Gaza confirmed to media that there were strikes in the area of Khan Yunis, at the southern tip of the Palestinian territory of two million inhabitants.
Israel's proposal to annex its settlements in the West Bank and the Jordan Valley form part of a broader US peace plan released in January.
The proposals foresee the ultimate creation of a Palestinian state on the remaining West Bank territory and the Gaza Strip.
But the plan falls far short of Palestinian aspirations, with a state on reduced territory and without occupied east Jerusalem as its capital.
Hamas and Israel have fought three wars in recent years, with the latest conflict in 2014 killing 2,251 Palestinians.
There are no official relations between the two sides.
The Palestinian Authority, a separate administration based in the West Bank, cut its cooperation with Israel last month.