Two Hamas fighters injured in Gaza training explosion
The accident came as Hamas urged that giving up their weapons would not be an option while efforts to reconcile with rival Fatah Party continue after a decade-long split.
"No one in the universe can disarm us. On the contrary, we will continue to have the power to protect our citizens," Hamas' Gaza head Yahya Sinwar said during a speech to Palestinian youth on Friday.
"No one has the ability to extract from us recognition of the occupation."
The 50-year-old spymaster, who established the movement's security and intelligence network, was elected as the new head of Hamas in Gaza earlier this year.
Hamas and Fatah signed an agreement last week to end their split after talks in Cairo, with President Mahmoud Abbas calling it a "final" accord.
In a bid for stronger support, a high-ranking Hamas delegation began his visit to Iran on Friday to inform its backers in Tehran about reconciliation efforts with Fatah.
The group led by deputy chief Salah al-Aruri is due to meet senior Iranian officials.
This comes after Israel insisted it will not recognise any unity Palestinian government unless Hamas cuts off ties with Tehran.