The Iranian military questioned 15 detained British navy personnel Saturday and said they confessed to illegally entering the country's territorial waters, as Iran accused Britain of "blatant aggression."

Britain has demanded the return of the sailors and denied they had strayed into Iranian waters while searching for smugglers off Iraq's coast.

The eight Royal Navy sailors and seven Royal Marines were brought to Tehran for questioning, and a top military official, Gen. Ali Reza Afshar, said they "confessed to illegal entry into Iran's waters."

"The said personnel are being interrogated and have confessed to aggression into the Islamic Republic of Iran waters," Afshar was quoted as saying by the semi-official ISNA news agency.

The British sailors had just searched a merchant ship when they and their two inflatable boats were intercepted by Iranian vessels Friday at around 10:30 a.m. near the disputed Shatt al-Arab waterway, U.S. and British officials said.

The Iranian vessels surrounded them and escorted them away at gunpoint.

The incident came at a time of heightened tensions over Iran's nuclear ambitions and allegations that Iran is arming Shia Muslim militias in Iraq. Still, Britain was treating it as a mistake rather than a provocation.

Both Britain and the European Union are calling on Iran to let the sailors go.

"We've sought a full explanation of what happened and left the Iranian authorities in no doubt that we expect the immediate and safe return of our service personnel and boats," said British Foreign Secretary Margaret Beckett.

Political motivation suggested

Rosemary Hollis, director of research at the London-based Institute of International Affairs, also known as Chatham House, said the incident may have been politically motivated, in light of what's happening at the United Nations this weekend.

The UN Security Council was scheduled to vote Saturday on more sanctions against Iran because of its nuclear program.

"Well, it's curious, because the British navy is maintaining that they were very definitely in Iraqi territorial waters, carrying out a mission approved by the UN and the Iraqi government," Hollis told CBC Newsworld.

"At the very least, for the Iranians, this will serve to send a message that what's going on in Iraq, with the U.S. and the British forces there, and what's going on in the region more generally, with the military deployment, is considered by Tehran menacing to them, a threat to them."

A former British marine, who along with seven others, was held captive by Iranians in a similar incident in 2004, said the current group of captive sailors are likely feeling a lot of uncertainty, partly because of the language barrier.

"No one will tell them what's happening," said Scott Fallon. "We had an interpreter who arrived on the second day who spoke relatively passable English. But up until that point, we didn't know who had us or what the reasons were or what they wanted."

In the incident three years ago, Iran seized six British marines and two sailors in the Persian Gulf. They were paraded in front of cameras, blindfolded. They were only released when they said they had entered Iran illegally.

With files from the Associated Press