Carles Puigdemont (left) and Jimmy Carter.

The setback comes in the wake of visits by both former Catalan premier Artur Mas and current regional premier Carles Puigdemont to the United States as part of concerted effort by separatists to drum up international support for their bid to hold a referendum on self-determination despite implacable opposition from Spain’s conservative central government on the grounds it is unconstitutional.

Sources in the Catalan government said the US embassy statement came at the request of Madrid

But both the US legation in Spain and the Carter Center on Thursday issued statements putting space between themselves and a cause which seen Mas and other top officials in the region banned from public office for their role in organizing a non-binding plebiscite on the independence issue in November 2014, held despite a Madrid-driven block from Spain’s Constitutional Court.

In its statement, the US embassy said Catalan independence was an “internal” matter for Spain and noted its position on the issue had not changed. The United States was “profoundly committed to maintaining relations with a united and strong Spain,” read the statement which noted Spain was “a vital ally” on issues ranging from “the promotion of mutual economic growth to the fight against Daesh [or so-called Islamic State] and the prevention of violent extremism.”

Meanwhile, following a meeting between former US president Jimmy Carter and Puigdemont, the Carter Center issued a communiqué saying that “neither President Carter nor the Center was able to become involved in the referendum process.”

In a further snub to Puigdemont, the foundation also chose to frame the meeting between Carter and the Catalan premier as a “reciprocal visit,” noting that the former US president had, in 2010, been the recipient of Catalonia’s Premi Internacional Catalunya award – an annual prize granted to those making a major contributions to science, culture or human values.

But sources within the Catalan government responded by saying that the US embassy statement had been clearly released “at the request of the Spanish government.” Those sources also said the mere fact the legation had issued a statement on the subject of Catalan independence signified that the secession process “forms part of the political and diplomatic agenda for the United States” and “is not an internal issue.”

The Carter Center said it would not become involved in the Catalan independence issue

The same Catalan government sources also brushed aside the Carter Center statement, noting the regional premier had not been seeking backing for a referendum from the former US head of state but had merely wished to inform him of the desire to do so.

In early April, the deputy premier of Catalonia, Oriol Junqueras, said that an official referendum on independence for the northeastern Spanish region would be called in June, stating that the country’s Constitutional Court did not have the authority to suspend it, as it had tried to do on April 4 by freezing funds from the regional budget that would be used to organize the poll.