Jack Straw has pressed his Tehran counterpart over eight Royal Navy sailors detained after apparently straying into Iranian waters.

The foreign secretary moved on Tuesday to ask for answers from the Iranian authorities over the incident.

But according to state-run television reports the men will face charges.

"They will be prosecuted for illegally entering Iranian territorial waters," the Arabic language Al-Alam station said.

A Foreign Office spokesman said: "We are trying to get the Iranians to explain exactly what they mean by that.

"They have got to come up with some answers to our questions and we are pressing them for answers."

The eight sailors and their three Navy patrol boats were seized in Iran on Monday after they strayed across the Iraqi border.

Iran's Revolutionary Guards said that three ships had illegally entered their territory on the Shatt al Arab river and the sailors were being questioned.

The Ministry of Defence confirmed that the sailors had been detained while "delivering a boat from Umm Qsar to Basra".

A spokesman said: "The team were travelling in three boats, two Boston whalers and one British Army combat support boat, along the Shatt al Arab waterway.

"The boats are unarmed but the crews were carrying their personal weapons."