Anti-Brussels campaigners accused the Labour leader of attempting to make “political capital out of the Paris shootings.”
Mr Miliband made the remark during a question-and-answer session with voters in Stevenage, Hertfordshire.
“Think about terrorism and counter-terrorism. We are much better working across borders to do that,” said the Labour leader, who attended the mass demonstration against terrorism and extremism in Paris on Sunday.
“Think about our economy… I just think we are much, much better working within the EU than not.”