Sinn Fein president Gerry Adams congratulated the pro-independence parties who won a clear majority in Catalonia's regional election.
The Louth TD described the result as an "inspiring demonstration of democratic power" after 1.9 million people backed separatists.
"There is now a clear mandate for an independent Catalan state and an unstoppable demand for a referendum on independence," he said.
"I urge the Spanish government to immediately enter into formal negotiations with Catalan representatives on this issue. The voice of the Catalan people must be heard."
