The Cornish station often deals with international distress calls

They were first contacted by the Panama registered El Safa when it broke down on 3 April. The Yemenis have apparently refused to let the crew land.

The captain again called on Thursday, saying they had been drinking "rusty tank water" for weeks and had no food.

The International Transport Workers Federation has been asked to try to get the local authorities to send help.

Falmouth often deals with international distress calls as it has the UK's only direct link to satellite station Goonhilly Down.

Once they have been checked the messages are passed on to the relevant rescue centre.

'Last resort'

That there was a second call from El Safa's captain - more than a month after the original distress signal was given - was unusual, said Falmouth deputy watch manager Pete Ritchie.

"He came back to us apparently as a last resort. We obviously could not let it go. It was a matter of letting a responsible authority know about it."

The vessel was also running low on fuel to run its generators, the captain told coastguards in a telephone call.

Its crew had not had contact with the boat's Panamanian owners for at least three days, said BBC correspondent Ed Goodridge .

He [the captain] came back to us apparently as a last resort. We obviously could not let it go Pete Ritchie, Falmouth Coastguards

When Falmouth first picked up a may day call from El Safa, which said it had broken down and was drifting, it passed the message to local search and rescue authorities.

"The vessel came back to say it had made contact with the Yemen, and they had promised to send help," said Mr Ritchie.

"They obviously towed them to some position offshore and they have been there ever since."

He said this kind of situation was unusual but not unheard of.

"A number of years ago a foreign vessel was impounded at Falmouth, and the crew ran out of food and water then. These situations are for the ship owners and the port authorities to sort out between them."

It is not known why the Yemeni authorities have denied the crew access to shore, or means to fix the engine, added our correspondent.