A Venezuelan Navy vessel threatened to "open fire" on a ship carrying humanitarian aid that was dispatched and financed by Puerto Rico's government, according to the island's governor.

In a statement Saturday night, Gov. Ricardo Rosselló said he instructed the ship, which departed the island Wednesday and had six American citizens on board, to leave the area where it was reportedly threatened by embattled President Nicolás Maduro's navy to ensure the crew's safety.

"This is a direct threat against a humanitarian mission being carried out by American citizens," he said. "This is unacceptable and shameful."

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Rosselló said he had notified U.S. government official about the alleged incident.

A spokesperson for the Puerto Rican government told CBS News the ship was entering Venezuelan territorial waters when it was threatened. The ship, carrying more than 200 tons of humanitarian aid, was heading to the port city of Puerto Cabello, in Venezuela's northwestern coast, the spokesperson added.

Although the spokesperson said the ship was registered with the island-nation of Vanuatu, a Telemundo journalist on board posted photos of the U.S., Puerto Rican and Venezuelan flags being displayed on the vessel.

Ya estamos de regreso en Bonaire con la ayuda humanitaria que no pudo entrar esta tarde a Venezuela.⁦@TelenoticiasPR⁩ pic.twitter.com/ol1Cs3LjMk — Jose Esteves (@jestevesT2) February 24, 2019

Republican Sen. Rick Scott of Florida, a state with one of the largest Puerto Rican communities in the nation, said the U.S. would not tolerate any threats against American citizens. "The U.S. will stand against the threats of gangs and thugs and will ensure the safety of our citizens!," Scott wrote on Twitter Saturday night.

.@Nicolasmaduro has now threatened U.S. citizens for attempting to help the people of #Venezuela and that will not be tolerated. The U.S. will stand against the threats of gangs and thugs and will ensure the safety of our citizens! https://t.co/cAqev1kn28 — Rick Scott (@SenRickScott) February 23, 2019

A State Department spokesperson told CBS News the agency was investigating reports of the alleged incident.

"The State Department has no higher priority than the safety and security of American citizens abroad," the spokesperson said. "We are looking into reports of this latest threat by Maduro against persons trying to deliver humanitarian aid to the Venezuelan people. Due to privacy considerations, we have no further comment at this time."

Saturday was a critical moment in the ongoing political standoff in Venezuela between Maduro's regime and the main opposition leader, National Assembly President Juan Guaidó, who is backed by the U.S. and a growing international coalition. Bold efforts by opposition officials, international workers and civilians to transport tons of foreign aid into Venezuela from its borders with Colombia and Brazil provoked deadly skirmishes.

According to the government of Colombia, a staunch U.S. ally which has taken in more than a million refugees from its crisis-stricken neighbor, dozens of Venezuelan soldiers defected and entered Colombia Saturday. Widespread defections among the ranks of the Venezuelan military, however, did not occur as some opposition officials had hoped for.

After accusing Colombia of "lending itself to an aggression against Venezuela," Maduro severed ties with the neighboring country and expelled its diplomats. Vice President Michael Pence will travel to Colombia Monday and call for Maduro's ouster.

Along with recognizing Guaidó and issuing sweeping sanctions against the largest state-owned oil company in Venezuela, the Trump administration has pledged more than $20 million in humanitarian assistance to the Venezuelan people.