Updated

American activists reached the halfway point in a long trek toward the U.S. naval base at Guantanamo Bay to protest treatment of terror suspects, but it appeared unlikely the communist government would let them enter a Cuban military zone to reach the U.S. outpost.

Marchers from the largely Christian group, Witness Against Torture, said by cellular telephone on Thursday that they had completed about half of the 50-mile trek from the eastern city of Santiago.

The 25 marchers, who set out Wednesday, hope to arrive at — or at least near to — the naval base by Saturday, which is International Human Rights Day. The march was organized by the Catholic Worker movement, an anti-war and social justice alliance.

"We don't know how far we can get, so every step forward is an amazing thing," said Shelia Stumph, a 28-year-old marcher from Raleigh, N.C.

If denied entry to the base, they have said they will fast and pray for the abolition of torture by all nations.

The U.S. government says the roughly 500 foreign terror suspects at Guantanamo Bay are enemy combatants, not prisoners of war, and are not entitled to the same rights afforded under the Geneva Convention. Critics say that leaves the door open to the use of torture.

Cuban officials, speaking on condition of anonymity because they were not authorized to speak to the press, said it was unlikely that the island's Revolutionary Armed Forces would allow marchers to traverse the miles-wide military zone that has surrounded the American base since shortly after the 1959 triumph of the Cuban revolution.

Cuba's elite Frontier Brigade considers its military zone its front line of defense against the United States, which it accuses of trying to undermine its government for more than four decades.

Permission to enter the area is rarely granted to civilians — especially foreigners — and even then only after months of deliberations.