Israeli tank fire has killed a Palestinian woman in the Gaza Strip, Palestinians say, in some of the worst clashes between Israeli forces and Hamas militants since 2014.
The woman was killed and another person was injured in the Khan Yunis area, southern Gaza, local medics said.
Israel said it was responding to mortar rounds fired by Hamas fighters.
The clashes came after Israel said it had discovered a new tunnel reaching into Israel from Gaza.
Israeli army spokesman Lt Col Peter Lerner said the tunnel was about 30 metres (100ft) below the surface.
In a statement, Israeli Defence Minister Moshe Yaalon said: "We will not be deterred by the Hamas threats, and continue our actions in the wake of the violation of our sovereignty, until the last of the tunnels is found and exposed."
The army said attacks by the militants were targeting Israeli forces searching for tunnels in the border area.
Meanwhile, Hamas militants warned that they "will not allow the continuation of Zionist aggression against the Gaza Strip".
Last month, the Israeli military said it had uncovered and "neutralised" a tunnel extending from Gaza several hundred metres into Israeli territory
Since Wednesday, Hamas and other Palestinian militant groups have fired guns and mortar rounds across the border, and the Israeli air force has carried out bombing raids.
The exchange of attacks continued on Friday.
In 2014, Israel and militants in the Hamas-controlled Gaza fought a devastating war that lasted 50 days.
Hamas fighters used tunnels to infiltrate Israeli territory on four occasions, killing 12 soldiers, while Israeli troops destroyed more than 30 tunnels.
The conflict left at least 2,251 Palestinians dead - including more than 1,462 civilians, according to the UN - and 11,231 injured. Some 18,000 homes in Gaza were also destroyed or badly damaged.
On the Israeli side, 67 soldiers and six civilians were killed, and up to 1,600 injured. Rockets and mortars launched from Gaza caused damage to homes and other buildings inside Israel.