The defence ministry announced Friday that it had concluded three agreements to buy 14 Lockheed Martin-made warplanes plus arms and training valued at 1.58 billion euros ($1.8 billion).

Hours later, Prime Minister Peter Pellegrini issued a statement saying that the contracts were invalid because they had not been approved by the finance ministry.

"Premier Pellegrini considers the contracts regarding the purchase of F-16 fighters signed earlier in the day by the defence ministry to be invalid for the moment, as the finance ministry still hasn't approved the deal," a statement said.

The defence ministry is headed by Peter Gajdos from the hard-right Slovak National Party (SNS), a junior coalition partner to Pellegrini's populist left SD-Smer Social Democracy.

Analysts suggested Friday that the clash was likely rooted in an internal power struggle within the coalition.

A former communist NATO and eurozone member of 5.4 million people, Slovakia is seeking to replace its ageing fleet of Soviet-designed, Russian made MiG-29 fighter jets.

The US State Department approved the F-16 deal in April. Pellegrini's government had formally decided in July to go ahead with the purchase.