A Dutch organisation has anchored a boat offering abortions off the Spanish port of Valencia, circumventing Spanish abortion laws and prompting protest from anti-abortion activists.

The boat, floating in international waters, offered terminations under the Netherlands' more liberal abortion laws on Friday.

About 100 members of Provida, the Spanish anti-abortion group, were in the port to protest the arrival, some shouting "assassins" and "no to abortion", Spanish media said.

Police formed a barrier between them and hundreds of pro-abortion activists to prevent incidents.

Speaking in support of women seeking abortion, Pilar Bardem, an actress, called for "respect" for women who had made the "very difficult" decision to terminate a pregnancy.

Spain decriminalised abortion in 1985 but only for certain cases - up to 12 weeks of pregnancy after a rape; up to 22 weeks in the case of malformation of the foetus; and at any point if the pregnancy represents a threat to the physical or mental health of the woman.

But Spain's Socialist government last month said it plans to introduce a law that will offer greater legal protection for women who wish to have an abortion and doctors who carry out the procedure.

The Women on Waves ship visited Ireland in 2001, Poland in 2003 and Portugal in 2004, sparking protests in each country.