US-based Venezuelan opposition supporters have parked two boatloads of humanitarian aid in Curacao, retreating from a bid to ship it to their country following a warning from the navy.
The shipments are part of a broader aid drive that aims to help Venezuelans suffering shortages and put pressure on President Nicolas Maduro amid a bloody political standoff.
The Midnight Stone supply ship, loaded with nine cargo containers, entered Willemstad harbor in Curacao - 65 kilometres from Venezuela's coast - on Sunday, AFP reporters saw.
One of the opposition supporters who disembarked from the ship, Nicola Stasi, said a Venezuelan navy frigate had sped towards the Midnight Stone as it approached Venezuelan waters on Saturday.
He said he had spoken by telephone from the boat with a Venezuelan naval commander.
"It was a respectful conversation but at one point he said: 'If you enter (Venezuelan waters), you will be attacked,'" Stasi told AFP.
"We decided to turn around for the safety of the cargo and the crew."
Venezuelans in Curacao have also loaded a further 50 tons of aid onto a separate ship, the Seven Seas.
Its captain Carlos Quintavalle told AFP on Sunday he would not sail for Venezuela with the shipment until authorities there open the border.
Venezuela frigate face-off
The sea shipments coincided with opposition efforts to truck aid into Venezuela by land.
That has led to bloody confrontations at the borders with Colombia and Brazil.
Maduro has branded Guaido's aid effort a "show" and a smokescreen for a US invasion.
He has closed Venezuela's sea border with Curacao to block the shipments.
Despite this, supporters of Venezuela's self-declared president Juan Guaido said the Midnight Stone sailed for Venezuela with 250 tons of aid.
They said it was chartered by the government of Puerto Rico, an unincorporated US territory.
Stasi said the cargo was taken in one ship from Puerto Rico and transferred to the Midnight Stone in the US Virgin Islands before heading for Venezuela.
He said the face-off with a Venezuelan navy frigate took place about 3:30 pm (1930 GMT) on Saturday.
Tensions were high as the overall aid effort had raised the prospect of an armed confrontation.
US President Donald Trump has not ruled out US military action over the Venezuela crisis.
As the aid boat approached Venezuela, "there was already talk that if there was an attack (by Venezuelan forces), there would be a response in our favor," Stasi said.
Hours later, the United States issued a stern warning over violence that erupted during efforts to truck aid across Venezuela's land borders.
Secretary of State Mike Pompeo said the United States would "take action" after Maduro's security forces fired on demonstrators.
Possible official US aid
Maduro's opponents have called on the military to drop its support for him.
They accuse Maduro of stealing last year's election and blame his policies for dire shortages of food and medicine and for hyperinflation.
But Maduro blames US policies and sanctions for Venezuela's economic woes.
He regularly accuses Venezuelans based in the United States and elsewhere abroad of plotting against him.
Separately, the administrator of the US development agency USAID, Mark Green, tweeted last week that he had visited Curacao and discussed possible cooperation with the island to channel official US aid to Venezuela.
An autonomous state within the Kingdom of the Netherlands, Curacao hosts a US military "forward operating location" that provides support for anti-drug operations in the region.
The island's government stressed that the US forward base would play no part in any aid operations.