BRUSSELS, March 8 (Reuter) European Union fishermen have not withdrawn from disputed international fishing grounds in the North Atlantic after Canada threatened to seize vessels, a European Commission spokesman said on Wednesday.

Canadian Fisheries Minister Brian Tobin said on Tuesday that the Spanish fleet had stopped fishing for Greenland halibut, otherwise known as turbot, and left the area off Canada's east coast.

"They are not retreating...some ships have stopped, some are going on," the Commission spokesman said.

The Spanish and Portuguese governments gave instructions to continue fishing on the Grand Banks as this is perfectly legal, the spokesman added.

On Monday, Canada issued an ultimatum to the EU fleet an estimated 40 to 45 Spanish and Portuguese vessels to leave the area or be seized.

Canada is trying to stop a surge in catches by EU vessels which it says are threatening stocks of one of the last commercial species in the region.

"Any (vessel) seizure would be in breach of international law," the spokesman warned.

But he said it was premature to talk about retaliatory measures.

The dispute flared up after the EU rejected its share of a 27,000 tonne 1995 quota for Greenland halibut fixed by the Northwest Atlantic Fisheries Organization (NAFO) and instead set itself a much higher limit.

The EU has already exceeded its 3,400 tonnes NAFO quota.