Negotiations with Iran to secure the release of 15 personnel have entered the "next phase" the prime minister and foreign security said today.
Following the Iranian government's refusal to meet any of the UK's demands, foreign secretary Margaret Beckett said the government was today choosing to increase diplomatic pressure by releasing data proving HMS Cornwall was in Iraqi waters.
There is "no doubt" the eight Royal Navy and seven Royal Marines sailors were in Iraqi waters operating under a UN mandate, giving Iran no justification for detaining the personnel.
But Iran has stated the detention of the naval personnel is not linked to any wider issues, the foreign secretary said.
Addressing the House of Commons, Ms Beckett said the government was "in a new phase" of diplomacy. This involves releasing details of the sailors' location and discussion between the UK and Iran for the public record.
The UK has also ceased all other bilateral business with Iran until the personnel are released and will keep its other policies towards Iran under review, the foreign secretary said.
Responding to prime minister's questions today, Tony Blair said Iran's actions were "completely unacceptable, wrong and illegal".
It is "time to ratchet up the international and diplomatic pressure", he agreed, and confirmed the UK is in talks with its international allies and partners. The Iranian government must realise it is "completely alone", the prime minister added.
Germany will denounce the act on behalf of the European Parliament, Mr Blair announced.
Ms Beckett also thanked the Iraqi foreign minister for already confirming the sailors were in Iraqi waters and calling for their release. The UK has also been in discussions with the US, Turkey and Saudi Arabia, the foreign secretary added.
Ms Beckett confirmed COBRA, the government's emergency committee, has been meeting daily since Friday's incident. The Foreign Office has also spoken several times with Iranian ambassadors, but Tehran has refused to meet any of the UK's demands to release personnel or disclose where they are being held.
Earlier today the Ministry of Defence (MoD) released evidence showing HMS Cornwall and the 15 sailors were in Iraqi waters at the time of the incident.
Downing Street said satellite images and GPS data showing the personnel were 1.7 nautical miles into Iraqi waters were "difficult to dispute".
At a briefing, vice admiral Charles Style explained the Iranians gave two conflicting sets of data, the first placing the sailors in Iraqi waters. When this was pointed out to Iran they returned with a second set of "correct" data showing them in Iranian waters.
The sailors were "ambushed" while going about their legitimate business and their detention was "unjustified and wrong", he said.
Iran has so far said the sailors are being well treated but has refused to confirm where they are being held or allow the sailors any contact with UK diplomats.
Turkey's prime minister Recep Tayyip Erdogan has been reported as saying Turkish diplomats may be allowed to meet the sailors.