The Health Ministry in Gaza has said a Palestinian man has died after being shot near a border fence by Israeli soldiers.
At least nine other men were reported to have been injured in the incident.
The Israeli army said it had first fired warning shots after a group of men approached the fence.
The man is the first to be killed since the ceasefire agreed between Hamas and Israel came into effect on Wednesday evening.
A Hamas spokesman accused Israel of violating the Egyptian-mediated truce and said the group would complain to Cairo.
An Israeli military spokeswoman said the army was checking reports of the incident.
Medics said a 23-year-old man was hit in the head by Israeli gunfire after he approached the security fence that runs along the Gaza frontier.
A relative of the dead man, who was at the scene, told Reuters that the victim had been trying to place a Hamas flag on the fence.
The relative said that an Israeli soldier had fired into the air three times before the man was hit in the head by a bullet.
Wednesday's ceasefire deal ended eight days of fierce fighting that left 163 Palestinians and six Israelis dead.
According to the terms of the accord, both Israelis and Palestinians agreed to stop their hostilities.
However, the brief document left details on access to the tense border zone to be worked out in the days ahead.
Seven other Palestinians have been wounded by Israeli gunfire from the border since the start of the ceasefire, medics said.
They were injured after the Israeli military said 200 Palestinian "rioters" approached the fence.
Israel's army constantly patrols the border area and says its forces have come under increasing attack this year, with militants planting explosive devices and firing an anti-tank missile on at least one occasion.
Israeli Arab arrested over Tel Aviv bombing
Israeli authorities arrested an Israeli Arab on suspicion of planting a bomb in a Tel Aviv bus that wounded 15 people.
Police also arrested a number of Palestinians affiliated with Hamas and Islamic Jihad militants in the Israeli-occupied West Bank on suspicion of having recruited the man to carry out the bombing.
Police spokesman Micky Rosenfeld did not give names or an exact number of how many people were in custody.
He said the Israeli Arab notified his Palestinian handlers in the West Bank when the bomb was in place on the commuter bus, and they then detonated the device with a mobile phone.
"The investigation is still under way, and other arrests are expected," the Shin Bet internal security service said in a statement.
The Israeli army said yesterday that 55 suspected Palestinian militants had been arrested in the West Bank, citing a need to maintain calm after a truce ended the Gaza fighting.