Argentina’s plans to nationalise private pension funds battered shares on Thursday in some of the country’s biggest foreign investors, as concerns rose that the government was preparing to expropriate its Spanish-owned national airline in a new market-unfriendly step.

Unconfirmed reports suggested the government would announce the expropriation this week or early next of Aerolineas Argentinas – the troubled Argentine flag carrier, which is owned by Spain’s Marsans group – a prospect that officials have suggested is possible.