"The British occupier forces did trespass our waters. Our border guards detained them with skill and bravery. But arrogant powers, because of their arrogant and selfish spirit, are claiming otherwise," IRNA quoted Ahmadinejad as saying during a speech in the southeastern city of Andinmeshk.
"Instead of apologizing over trespassing by British forces, the world arrogant powers issue statements and deliver speeches," Ahmadinejad told the crowd celebrating the Persian New Year holiday, IRNA said.
British Foreign Secretary Margaret Beckett urged Iran to resolve the crisis peacefully, saying London remains open to dialogue.
The British sailors were detained by Iranian naval units March 23 while patrolling for smugglers near the mouth of the Shatt al-Arab, a waterway that has long been a disputed dividing line between Iraq and Iran. Britain insists that the service members were in Iraqi waters. Iran has been saying the Britons were in Iranian waters and has demanded an apology.
Tehran appears intent on sending a message of strength as it faces mounting U.N. Nations sanctions over its uranium enrichment program, which the U.S. and other nations suspect the Islamic Republic is using to develop nuclear weapons.
On Thursday, Ahmadinejad accused Britain of trying to solve the crisis through propaganda and not diplomacy, state TV reported.
An Iranian diplomat said earlier Saturday that the case had entered a legal phase, according to the news agency.
IRNA said on its Web site that Gholam-Reza Ansari, the Iranian ambassador to Russia, had told Russian television Vesti-24 that, "the case of the detention of British sailors has taken on a judicial form."
IRNA originally quoted the ambassador Saturday morning as saying the sailors could be "tried if there is enough evidence of guilt." But the agency published a correction later claiming Ansari's comments were incorrectly translated by Russian television. The Russian TV station made no comment.
Britain has frozen most contacts with Iran and referred the issue to the U.N. Security Council, which expressed "grave concern" on Thursday over Iran's seizure last week of the Britons.
Moderate former Iranian President Mohammed Khatami told reporters on Saturday that he hopes the current standoff will be resolved peacefully "instead of facing a new disaster not only for Iranian-British relations, but for Iran internationally."