A Palestinian man has been shot dead by Israeli soldiers close to the Gaza border, Palestinian officials say.
It is the first reported killing since the ceasefire between Hamas and Israel came into force on Wednesday evening.
The Israel Defense Forces (IDF) said it fired warning shots at a group walking towards the border fence, then fired at their legs when they did not respond.
Earlier, Israel said it had arrested several people over a bus bomb in Tel Aviv on Wednesday.
The blast, which injured 29 people, came hours before the ceasefire began and was the first such attack in Tel Aviv for more than six years.
The shooting on Friday, east of Khan Younis, reportedly happened around the no-go area surrounding the Gaza border fence.
A man in his 20s, named as Anwar Qdeih, was killed and at least 10 other people injured, said the health ministry in Gaza.
A relative of Mr Qdeih told Reuters news agency that he had been trying to place a Hamas flag on the fence. The army fired into the air three times before he was shot in the head, the relative said.
Israel said a group of about 300 people had approached the fence and that some had attempted to break through.
The soldiers shot at their legs after warning shots were ignored, the IDF said.
Following the incident, IDF spokeswoman Avital Leibovich tweeted: "Trying to breach Gaza fence in order to enter Israel is breaking ceasefire."
Hamas officials said the shooting was an Israeli violation of the Egyptian-brokered ceasefire.
Hamas "will raise this violation with Egyptian mediators to make sure that it does not happen again", spokesman Sami Abu Zuhri told AFP news agency.
Palestinian Foreign Minister Riad Malki also said it was "a clear violation of the agreement and should not be repeated".
Israel launched its offensive in Gaza - which it says was aimed at ending rocket fire from Palestinian militants - with the killing of a Hamas military leader last week.
Provisional UN figures say that 158 people were killed in the Gaza Strip during the violence.
Four Israeli civilians and two soldiers were killed - the second of the military casualties died of his wounds on Thursday.
Under the truce deal, Israel has agreed to end all hostilities and targeted killings of militants, while all Palestinian factions will have to stop firing rockets into Israel and staging border attacks.
Details regarding the border region, which is regularly patrolled by the Israeli military, have yet to be worked out.
The Hamas Prime Minister in Gaza, Ismail Haniya, has urged Gazans to respect the truce.
The BBC's Jon Donnison in Gaza says shootings near the border happen fairly often and do not always lead to an escalation of violence.
Israel has unilaterally declared a 300m-wide exclusion zone around the fence which it says is needed for security but which Palestinians say steals valuable farming land.
How far this latest clash goes will depend largely on how Hamas chooses to respond, our correspondent adds - it is a reminder, though, that the ceasefire is very fragile.
Earlier on Friday, Israel's security agency Shin Bet said in a statement that the arrests relating to the bus bomb had happened "a few hours after the attack", AFP news agency reported.
Israeli military spokeswoman Avital Leibovich said the suspect was "an Arab-Israeli from Taybe and a member of Hamas".
Officials said that a number of Palestinians affiliated with Hamas and Islamic Jihad in the West Bank were also arrested, suspected of having recruited the man to carry out the bombing.