EU fishermen were equally guilty, EU Fisheries Commissioner Joe Borg said, adding that a priority was to change rules so that non-EU vessels could be prevented from landing catches at EU ports if they were quota-busting or catching undersized fish.

"IUU is internationally a very big problem," he told reporters. "We need to have measures which we can implement in our own waters, as a lot of IUU fish ends up on our markets."

"We are proposing that an EU port will have the obligation to require certification from a third-country (non-EU) flagged vessel that the fish it has in the hold are legally caught."

That certification would have to be issued by the country whose flag the vessel concerned was flying, he said. If there were any doubts whether certificates were genuine or being handed out improperly, EU inspectors would act, he said.

Sanctions might include closing ports to vessels found in breach of EU rules, he said.

A lot of IUU fishing is done by vessels flying so-called flags of convenience where scrutiny by local authorities can often be minimised, officials say.

Historically, IUU fishing involves practices such as disregarding requirements to obtain catch licences, exceeding quotas, ignoring closed fishing areas, using non-authorised fishing tackle and catching undersized fish, among others.

"We will be carrying out checks," Borg said. "If suspicion is aroused that a certain flag state is dishing out certificates when they are not backed by the facts, there is the possibility of blacklisting," he said.