An Israeli soldier has been killed and four others injured by so-called friendly fire near to the Gaza border, the Israeli military says.
The incident happened while the soldiers were involved in a clash with Palestinian militants in Gaza.The army said the group had been trying to plant explosives underneath the security fence along the border.
The clash follows a month of increased tension along the Gazan border with frequent exchanges of fire.
Witnesses in Gaza earlier told news agencies they had heard loud explosions close to the border, a short distance from the Nirim kibbutz on the Israeli side.
The Israeli military initially said four soldiers had been injured.
But they later said the men, who were part of a group patrolling the border, had been hit by Israeli fire. It also said one had died.
"The soldiers were hit by a stray mortar shell fired by Israeli forces as they engaged with Palestinian militants along the border," an army spokesman said.
The army said it was investigating the incident.
Increased activity Earlier this week, two Palestinian men were shot dead at the Gaza border - Israel said they had been attempting to break through the security fence but this could not be independently verified.
In recent weeks there has been an increase in activity around the border area, with Palestinians firing rockets into Israel, and the Israeli army carrying out regular air strikes on Gaza.
Israel says it holds Hamas, which controls the Gaza Strip, wholly responsible for all of the rockets fired across the border.
But the BBC's Jon Donnison in the West Bank says many of the attacks are carried out by smaller militant groups, and it is unclear whether Hamas has the power to prevent them.
Earlier on Friday, Israeli soldiers shot dead an elderly Palestinian man in his bed, in the West Bank city of Hebron.
Amr Qawasme, who was in his 60s, was killed in what is thought to have been a case of mistaken identity during a series of raids to capture members of Hamas.
He was neighbour of a Hamas member who had been released from prison the day before.
Israel said Mr Qawasme was innocent and that it regretted the incident. An investigation is being carried out.