Rockets like this one aimed at Ashkelon, Israel are still being fired
Hamas says continuing rocket fire by Palestinian militants from Gaza into Israel is "ill-timed".
Hamas, which runs Gaza, said it had nothing to do with the attacks and would act against those responsible.
The warning, issued in a brief statement, was released as Egyptian-led efforts continue to achieve a long-term ceasefire between Hamas and Israel.
A key Israeli condition of any deal is the complete cessation of Palestinian rocket attacks against Israel.
Hamas has fired thousands of rockets into southern Israel over the past few years.
In eight years, around 20 Israeli civilians have been killed by rockets, and dozens injured.
'Right to resist'
This was Israel's justification for its recent, massive military operation in Gaza, in which around 1,300 Palestinians are thought to have died.
"Hamas is under pressure to make the conditions right for a ceasefire deal with Israel," says the BBC's Aleem Maqbool in Gaza.
A senior leader of the Islamic Jihad movement, Khader Habib, confirmed to the BBC that Hamas forces had arrested some of the group's members for launching rockets.
Islamic Jihad said they were only released when they signed forms saying they would no longer carry out attacks.
Mr Habib said Islamic Jihad had "the right to resist" and would continue to fire rockets in response to what it saw as any aggression from Israel.