* EU says Iceland's unilateral fishing decision worrying
* Iceland says it is not party to any global agreement
(Adds Iceland government comment, background)
BRUSSELS, April 2 (Reuters) - The European Commission and Iceland clashed on Thursday over mackerel fishing plans, souring relations at a time when the North Atlantic island is considering whether to apply to join the European Union.
The commission said Iceland's plans to boost mackerel fishing contradicted global agreements on reviving depleted stocks, but Reykjavik said it is not party to such an accord.
The European Union's executive arm said it was worried by Iceland's unilateral decision to set its fishing quota for mackerel at 112,000 tonnes in 2009.
Hrefna Karlsdottir, Iceland's permanent secretary at the Fisheries Ministry, said Iceland had not broken any international deals as it was not party to any.
She said the island had repeatedly requested to be a partner in the management of mackerel stocks in the Northeast Atlantic.
"We have deliberately been kept out of the management of these stocks," Karlsdottir said. "We have therefore not recognised the agreements reached within the North East Atlantic Fisheries Commission and are not bound by them."
Fishing is seen as the biggest obstacle to Iceland joining the EU, should the island apply for membership.
Ahead of an election later this month, Iceland's interim government is split on the EU, with the popular Left-Greens against it and the more centrist Social Democrats in favour.
The European Commission said in a statement Iceland's quota would result in a complete reversal of the improved trends in the mackerel stock and would nullify the conservation efforts.
The global financial crisis has hit Iceland hard, increasing the importance of its fishing industry.
The country's powerful fishing lobby believes sovereignty would be at risk if the EU forced the island to open its waters to foreigners. Many in Iceland, which waged "cod wars" against Britain over fishing rights in the 1970s, agree.
Warmer temperatures in the sea off Iceland's coastline have brought larger mackerel stocks further north, and according to Iceland's fisheries ministry, within its "fishing limits".
In a sharply worded letter to Norway published last month, Iceland said it had a "full right" to catch mackerel within its fishing limits.