Venezuelan officials said Tuesday that the country is banning air and sea trips to and from three Dutch Caribbean islands a region that has been linked to efforts to undermine President Nicolas Maduro by sending emergency aid to the South American nation.

The indefinite shutdown of the “maritime border” applies to commercial and fishing boats between Venezuela and the islands of Curacao, Aruba and Bonaire, said Falcon state’s civil protection director, Gregorio Jose Montano.

Aruba is a small island just north of Venezuela. It’s a constituent country that’s part of the Kingdom of the Netherlands, as it used to be a colony on the European land. It comes as opposition leader Juan Guaido has been rallying international support for his challenge to Maduro. Guaido has called for international emergency aid for Venezuela, including from Curacao, about 40 miles from Venezuela.

Maduro is vowing to block aid from entering Venezuela, saying the effort is part of a US-led coup attempt. Dutch officials have said they are opening Curacao as a hub for emergency shipments.

Guaido says he is organising caravans to try to bring in emergency food and medicine provided by the United States and other countries starting Saturday. Such attempts are also expected to come through Brazil and the Colombian border city of Cucuta, where supplies are being warehoused.