Puerto Rico nat'l park is site of Obama protest

A boy stands by a poster showing President Barack Obama and former President John F. Kennedy, a day before Obama's visit to Puerto Rico, on the grounds of El Morro National Park in San Juan, Puerto Rico, Monday June 13, 2011.  Obama's June 14 trip marks the first visit to the U.S. Territory by a sitting U.S. President since Kennedy's 1961 visit. (AP Photo/Ramon Espinosa)
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A boy stands by a poster showing President Barack Obama and former President John F. Kennedy, a day before Obama's visit to Puerto Rico, on the grounds of El Morro National Park in San Juan, Puerto Rico, Monday June 13, 2011. Obama's June 14 trip marks the first visit to the U.S. Territory by a sitting U.S. President since Kennedy's 1961 visit. (AP Photo/Ramon Espinosa)

SAN JUAN, Puerto Rico (AP) — About 20 pro-independence demonstrators have kept an all-night vigil at a colonial fort in Puerto Rico to protest during President Barack Obama's visit to the island.

Demonstrators are on the grounds of the San Cristobal Fort on the edge of Old San Juan. The fort is part of the U.S. National Park system. Obama is expected to pass the area on his way to a meeting with the governor.

Protesters are calling for the release of three Puerto Rican nationalists imprisoned in the U.S.

Police said Tuesday that protest is peaceful and there have been no arrests.

A small but vocal minority in Puerto Rico favors independence. Island residents have voted consistently to maintain ties to the U.S.