BERLIN, Germany (Reuters):

Iran is considering charging 15 British sailors with illegally entering its waters and slated talks to discuss their seizure with London yesterday.

"The charge against them is the illegal entrance into Iranian waters and this issue is being considered legally," Iranian Foreign Minister Manouchehr Mottaki told reporters at the United Nations.

Tehran should be under no illusion how seriously Britain considers the detentions, Prime Minister Tony Blair said. He denied the navy personnel had been in Iranian waters.

"This is a very serious situation and there is no doubt at all that these people were taken from a boat in Iraqi waters," Blair told reporters after a European Union summit in Berlin.

Iran captured the 15 British Navy personnel at the mouth of the Shatt al-Arab waterway, which marks the southern stretch of Iraq's border with Iran, in the Gulf on Friday.

Britain said two boatloads of Royal Navy sailors and marines had searched a merchant vessel on a U.N.-approved mission in Iraqi waters when Iranian gunboats encircled and captured them.

"The Iranian authorities intercepted these sailors and marines in Iranian waters and detained them in Iranian waters and this has happened in the past as well," Mottaki said.

The incident raised tensions that were already high with the West over Tehran's nuclear programme. The U.N. Security Council imposed new sanctions on Iran on Saturday. London and Washington have also accused Tehran of fomenting violence in Iraq.

"They should not be under any doubt at all about how seriously we regard this act, which was unjustified and wrong," Blair said in his first statement since the sailors were seized.

Unlike the United States, Britain has diplomatic relations with Iran. But Blair had initially refrained from commenting publicly on the capture to avoid raising the stakes with Tehran.