* Measures to take effect a week after official publication
* Faroese ban a step towards measures against Iceland
* Iceland, Faroe Islands say EU breaking international sea law (Updates with reaction from Faroe Islands)
By Barbara Lewis
BRUSSELS, Aug 20 (Reuters) - EU authorities banned imports of herring and mackerel from the Faroe Islands on Tuesday and said they would prevent some Faroese boats from docking in EU ports, escalating tension in a dispute about alleged over-fishing.
EU officials have said the Faroese sanctions are a first step towards similar measures against Iceland in a long-running argument over how much mackerel should be caught. The spat has drawn comparisons to the "cod wars" of the 1950s and 1970s, and helped to derail Iceland's EU membership bid.
As the threat of sanctions loomed last week, Iceland and the Faroe Islands accused the European Union of violating international maritime law.
Faroe Islands Prime Minister Kaj Leo Holm Johannesen on Tuesday said the European Union's "coercive economic measures" could undermine regional talks on herring management, scheduled for next month.
The European Commission, the EU executive, said it had to act to protect a fish stock referred to as the Atlanto-Scandian herring.
"The imposition of such measures is always done as a very last resort. The Faroese could have put a stop to their unsustainable fishing but decided not to do so," European Commissioner for Maritime and Fisheries Affairs Maria Damanaki said in a statement.
The measures endorsed on Tuesday have to be officially published, which is expected to take place over the coming days, and will take effect seven days later.
As well as the ban on herring and mackerel fish caught by Faroese vessels, they stop the islands' vessels from docking in EU ports, except in the event of an emergency.
The Commission said it had done its best to find a negotiated solution after the Faroe Islands awarded itself a quota that more than trebled its previously agreed share of the Atlanto-Scandian herring stock.
The Faroe Islands is a self-governed territory within the Danish Realm and not part of the European Union.
Until this year, the Atlanto-Scandian herring stock was managed jointly by Norway, Russia, Iceland, the Faroe Islands and the European Union.
The five meet on September 2-3 in London to debate herring management.
The Faroese prime minister said the EU sanctions broke the U.N. Convention on the Law of the Sea and might make it more difficult for the parties to reach an agreement at the meeting. (Editing by John O'Donnell and Andrew Heavens)