Speaking about counter-terrorism at the G7 summit in Sicily, the PM will say more pressure should be put on tech companies to remove extreme material.
They should report such content to the authorities, she believes.
Labour leader Jeremy Corbyn is to say the "war on terror" is not working.
In a speech in London as general election campaigning resumes after the Manchester suicide bomb attack, Mr Corbyn will point to links between wars abroad and "terrorism here at home".
