Hamas said last month it intended to implement the death penalty
The Hamas authorities in the Gaza Strip have confirmed that two Palestinian men have been executed for collaborating with Israel.
The Islamist movement did not say how the executions were carried out, but one Palestinian rights group said they had been killed by firing squad.
The mens' bodies were taken to Shifa hospital in Gaza City overnight.
This is the first time Hamas has implemented the death penalty since it took power in Gaza in June 2007.
Hamas Interior Minister Fathi Hammad said last month that the authorities intended to implement the death penalty for people found guilty of working with Israel.
The two executed men were convicted of treason and spying for Israel in February last year. They have been named as Naser Abu Furaih and Mohamad al-Sabaa.
Hamas's head of judicial military affairs, General Ahmad Attallah, confirmed the executions in a statement on the website of Gaza's interior ministry.
He did not say how the men were executed but, according to the AFP news agency, Samir Zakut of the Palestinian human rights group Al-Misan said they executed by firing squad before dawn.
An employee at Shifa hospital was quoted by the Associated Press as saying that the bodies of the two men, dropped off by armed men in the early hours, were riddled with bullets.
Technically, nobody can be executed in the Palestinian territories without the approval of the Palestinian President Mahmoud Abbas. But Hamas does not recognise Mr Abbas's authority.
The BBC's Jon Donnison, in Gaza, says this is a further sign of tensions between the Islamist group and Mr Abbas's secular party which runs the Palestinian-controlled areas of the West Bank.
Amnesty International, the human rights organisation, condemned the killings.
"Today's executions are an extremely retrograde step by Hamas," Deputy Director for the Middle East, Hassiba Hadj Sahraoui said.
"We are gravely concerned for the other Palestinian prisoners in Gaza who have been given death sentences by military courts."