San Juan: Republican presidential hopeful Rick Santorum left a trail of controversy in Puerto Rico after reportedly saying English should be the Spanish-speaking Island’s main language if it wants to be a US state.

With Puerto Rico holding a Republican primary on Sunday, his remarks touched a nerve at a time when every delegate counts in the close race to choose a candidate to run against President Barack Obama in November.

"It's a grave mistake," said Governor Luis Fortuno, a conservative who has endorsed former Massachusetts governor Mitt Romney but received Santorum when he arrived on the island on Wednesday.

Parents in Puerto Rico "want their children to speak their native language and English," Fortuno said.

In an interview published on Thursday, Santorum said that for Puerto Rico to become a state, federal law requires that English be the main language.

On Thursday, Santorum clarified his statement by saying that "English has to be learned as a language and this is a country where English is widely spoken and used."

"Obviously Spanish is going to be spoken here in the island, but this needs to be a bilingual country, not just a Spanish-speaking country," he said.

Spanish and English are both official languages of Puerto Rico.

Fortuno, who supports statehood, has called a referendum on the island's status in November, and Santorum's remarks are likely to play to fears among Puerto Ricans that statehood could lead to a loss of language and culture.

The issue of whether to seek statehood, independence or maintain the island's current status as a self-governing "commonwealth" has long dominated Puerto Rican politics.

In four earlier referenda, Puerto Rico voters chose to maintain the current status in Spanish dubbed a "Free Associated State."

In Sunday's primary, 20 delegates to the Republican national convention are up for grabs.

Following Santorum to Puerto Rico in search of delegates is Romney, who is due to arrive in the next days but whose campaign is already at work distributing campaign material in Spanish.

(Agencies)