HAVANA (Reuters) - Anti-war activist Cindy Sheehan defied a U.S. ban on travel to communist Cuba and flew to Havana on Saturday to join protesters demanding the closure of the Guantanamo prison camp for terrorism suspects.

Sheehan and four other American peace activists arrived in Havana and will join 10 others on a march to the U.S. naval base in eastern Cuba where about 395 suspected al Qaeda and Taliban fighters are being held.

The march is part of planned international protests against the prison camp on Thursday, five years after it opened with the first detainees flown in from the U.S.-led war in Afghanistan that followed the September 11 attacks.

Washington has faced steady criticism over the Guantanamo prison from rights groups and foreign governments because most of the prisoners have not been charged and due to reports of abuse of prisoners.

Americans who travel to Cuba without special licenses from the U.S. government can be punished with fines of thousands of dollars.

"I'm not afraid. What is most important is the inhumanity that my country is perpetrating in Guantanamo," Sheehan told reporters on arrival in Cuba.

"If I worried about reprisals I wouldn't be doing anything. ... I think it is time for people to step up and try to stop this," she said.

Cuba's government -- which has long condemned the prison as a concentration camp run by its political enemy the United States -- has allowed the protesters to march to the Cuban security perimeter surrounding the U.S. enclave.

The United States has said it does not use torture and that the camp was necessary to deal with the particular circumstances of its war on terrorism.

The U.S. military has quickened the pace for releasing captives held at Guantanamo. The Pentagon said in December the prison's population was now about 395 inmates, out of more than 770 who have been held there since the camp opened in January 2002.

The group of 12 marchers will include former detainee Asif Iqbal, a British citizen who was released after two years with no charges, and the mother of current prisoner Omar Deghayes, a British resident.

Sheehan, whose son was killed in the Iraq war, became a central figure in the U.S. anti-war movement last year after she camped outside President George W. Bush's Texas ranch and has been arrested at least three times at protests.

"We're here as American citizens to say that this prison needs to be shut down," said fellow peace activist Ann Wright, a retired U.S. colonel and diplomat who resigned over the invasion of Iraq.