British Prime Minister Tony Blair warned Iran on Sunday that the fate of 15 British sailors and marines seized off the Iraqi coast was a "fundamental" issue for his government, as Tehran suggested the group may be put on trial for violating Iranian waters.
British Foreign Secretary Margaret Beckett spoke by telephone with Iranian Foreign Minister Manouchehr Mottaki late Sunday, and reiterated London's position that the British sailors and marines were operating in Iraqi waters.
She asked that British diplomats be allowed to meet with the sailors and demanded their safe return, the Foreign Office said. In Jerusalem, U.S. Secretary of State Condoleeza Rice also called for their release.
"The detention of British sailors and marines by the Iranian government is becoming increasingly provocative the longer the troops remain in Iranian custody and has the potential of escalating to a military confrontation with so many U.S. and British troops and aircraft carriers in the Gulf," said CBS News foreign affairs analyst Pamela Falk.
"Signaling the continuation of the standoff, the Iranian Foreign Minister said at a press conference in New York on Sunday that Iran is considering charging the British troops with illegally entering Iranian waters," Falk reported.
At a European summit in Berlin, Blair said Iran's claim that the sailors had crossed into Iranian territorial waters "is simply not true."
"I want to get (the situation) resolved in as easy and diplomatic a way as possible," Blair said, but added he hoped the Iranians "understood how fundamental an issue this is for the British government."
On a visit to the Middle East, Rice told reporters that the sailors and marines should be released immediately and said "we all fully trust the British" that the service members were not in Iranian waters when they were seized Friday.
But the Iranians also stuck by their view that the British had violated Iranian territory.
"The Iranian authorities intercepted these sailors and marines in Iranian waters and detained them in Iranian waters. This has happened in the past, as well," Mottaki said in Persian through a translator.
"The charge against them is illegal entrance into Iranian waters," Mottaki said. "In terms of legal issues, it's under investigation."
Mottaki declined to provide the exact coordinates of where the Britons were seized, saying this "very detailed information has been submitted to the representatives of the United Kingdom."
A spokesman for Britain's defense ministry said they were not releasing the coordinates.
British, Israeli and Saudi media reports on Sunday suggested that Iran was hoping to trade the captured Britons for Iranian officials it claims have been abducted by the West in recent months.
Britain and the United States have said the sailors and marines had just completed a search of a civilian vessel in the Iraqi part of the Shatt al-Arab waterway when they were intercepted by the Iranian navy.
Iranian state news agency IRNA said British Ambassador Geoffrey Adams had spoken in Tehran with Ibrahim Rahimpour, the foreign ministry official in charge of western Europe, and asked about the condition of the British sailors and marines.
He was told by Rahimpour that they were "well and sound" and that "legal proceedings" were under way in their case. No other details were provided.
According to IRNA's English-language Web site, Adams said during the meeting that the British service members had been deployed in Iraq to establish security, and had no hostile intention toward Iran.
"Tehran has always exercised self-restraint in the face of border violations by the British troops," Rahimpour was quoted as saying. But after the "contradictory statements" in the seizure of the British, the case "required an inquiry into such suspicious events."
Lord Triesman, a Foreign Office under-secretary who had held talks with Iran's ambassador on Saturday, told Sky News there was good evidence the men were in Iraqi waters, but that the issue of whether the sailors had strayed into Iranian waters was only a technical one.
"I've been very clear throughout that the British forces do not ever intentionally enter into Iranian waters," he said. "There's no reason for them to do so, we don't intend to do so and I think people should accept there's good faith in those assertions."
Iran's top military official, Gen. Ali Reza Afshar, said on Saturday the seized Britons were taken to Tehran for questioning and had confessed to what he called an "aggression into the Islamic Republic of Iran's waters." He did not say what would happen to them but said all were being treated well and were in good health.
Tehran has described the incident as a "blatant aggression," but Britain has repeatedly insisted the sailors were in Iraqi waters in the Shatt al Arab waterway between Iraq and Iran.
The EU also has been pushing hard diplomatically to secure the sailors' release. Germany, which holds the EU's rotating presidency, had its ambassador in Tehran raise the issue with the Iranian government.
Rajanews.com, a Persian Web site of supporters of Iranian President Mahmoud Ahmadinejad, quoted a senior diplomat as saying the Britons were still being held by Iranian armed forces and would not be released until they promised "not do similar things in future."
The capture and detention of the British service personnel risks escalating an already fraught relationship between Iran and the West.
The U.N. Security Council of Saturday agreed to moderately tougher sanctions against Iran for its refusal to meet U.N. demands that it halt uranium enrichment. Many in the West fear Tehran's nuclear program is not for power generation but for arms making, a claim Iran denies.