Spain and Argentina were at diplomatic daggers drawn on Saturday as the two countries traded barbs over drug taking and economic decline.

Poor relations between the Hispanic nations hit a low on Friday night when Spain's Transport Minister Oscar Puente suggested Argentina's President Javier Milei was on drugs.

Milei's office responded on Saturday by accusing Spain's Socialist Prime Minister Pedro Sanchez of bringing "poverty and death" to his people and threatening Spain's unity.

The spat comes two weeks ahead of a visit to Spain by Argentina's "anarcho-capitalist" president. He will attend an event of the far-right Vox party and will be avoiding the Socialist head of government. The two have never had good ties.

Sanchez supported Milei's rival Sergio Massa in the election that brought Milei to power in December and not contacted Milei since the victory. Vox leader Santiago Abascal went to Buenos Aires for Milei's investiture.

Milei's anger this time appears to have been sparked by comments by Spain's transport minister linking the president to drug taking.

"I saw Milei on television" during the campaign, Puente told a Socialist Party conference on Friday. "I don't know if it was before or after the consumption... of substances."

He listed Milei among some "very bad people" who have reached high office.

Within hours, Milei's office issued an official statement lambasting Spain's prime minister.

"Sanchez put the middle class in danger with his socialist policies that bring only poverty and death," said the statement.

The government had also "endangered the unity of the kingdom" by making a deal with a separatist party to be able to stay in power.

Spain reacted with fury.

"The Spanish government categorically rejects the unfounded words... which do not reflect the relations between the two countries and their fraternal people," the Spanish foreign ministry said.

"The government and the Spanish people will continue to maintain and strengthen their fraternal links and their relations of friendship and collaboration with the Argentine people, a desire shared by all of Spanish society," the statement added.

Milei will travel to Spain in two weeks for an event on May 18 and 19 organised by the far-right opposition party Vox, which is in a race with the Socialists in next month's European elections.

He is not scheduled to meet Sanchez or Spain's monarch.