"Plans had been made to hold a press conference on board the group's ship the Rainbow Warrior in Bushehr, Iran, to present the results of research into different energy options for Iran which would allow it to meet its energy needs without recourse to nuclear power," a statement said.

"However, at the last minute with the ship on the edge of Iran's territorial waters, final permission to enter was withheld by the Iranian authorities," Greenpeace said without indicating whether any reason had been given.

"We are disappointed not be able to present our case in person to the people of Iran. At a time of massive naval operations in the Gulf it is a real shame that there appears to be no place for a peace ship."

There was no immediate word from the Iranian authorities.

The planned Bushehr press conference was one of a series of events that Greenpeace has been holding around the Middle East as part of a campaign for a nuclear-free region.

The group also held a protest outside parliament in Israel, widely believed to have the region's only nuclear arsenal.

Iran insists that the reactor Russia is building for it in Bushehr is for peaceful energy purposes only. But Iran's efforts to master the nuclear fuel cycle have raised fears in the West that the civil nuclear programme might be cover for an attempt to build a bomb.

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