Greenpeace activists have vowed to carry on their blockade of the country's biggest military port for as long as a month in an attempt to stop Britain waging war on Iraq.

The group's flagship Rainbow Warrior dropped anchor at Marchwood in Southampton, obstructing its entrance, on Monday morning.

Protesters chained themselves to two military supply ships, draping banners and painting "No War" slogans on the hulls, before three were arrested by Ministry of Defence police.

The Ministry of Defence (MoD) says the protest has delayed the departure of one of the ships, the Magdalana Green, which was due to join the Royal Navy task force led by the HMS Ark Royal on Monday.

We don't think civilians should die just because Americans can't be bothered to drive cars that are more fuel-efficient Blake Lee-Harwood, Greenpeace

On Monday evening a fourth woman remained strapped to the sonar dome on the hull of the Magdalana Green, while two of the protesters had been released without charge.

Blake Lee-Harwood, Greenpeace campaigns director, said: "As long as the Rainbow Warrior is there it is not going to allow any ships to go out or any ships to come in.

"We are prepared to stay here a very long time as we have a fundamental moral objection to an attack on Iraq, which will result in catastrophic civilian casualties.

"Ultimately this is a war about oil and we don't think civilians should die just because Americans can't be bothered to drive cars that are more fuel-efficient."

Activists tied themselves to the ships in protest

According to the MoD, the 25 or so protesters aboard the Rainbow Warrior are not breaking the law.

An MoD spokeswoman told BBC News Online: "It is a peaceful protest and was quickly identified as not being a terrorist threat.

"The protesters are not breaking the law.

"The Rainbow Warrior is in the approaches of Marchwood port which is not MoD property."

At an earlier protest at Marchwood on Saturday, children let off hundreds of balloons covered in peace messages.