Qatar's foreign minister has dismissed reports of threats of military action by Saudi Arabia over Doha's plans to acquire the Russian-made S-400 air defence system, saying Qatar's decision to buy weapons is a "sovereign" one.

The threats, Mohammed bin Abdulrahman Al Thani said on Monday, violates "international law and all the international norms".

"The purchase of any military equipment is a sovereign decision that no country has anything to do with," Al Thani told Al Jazeera.

In a letter addressed to French President Emmanuel Macron, Saudi King Salman expressed his "profound concern" with talks under way between Moscow and Doha for the sale of the advanced anti-aircraft weapon system, French daily Le Monde reported on Friday.

The Saudi monarch, who asked that France increase its pressure on Qatar, said he was worried about the consequences of Doha's acquisition of the mobile surface-to-air missile system, which he said threatened Saudi security interests.

"[In such a situation], the Kingdom would be ready to take all the necessary measures to eliminate this defence system, including military action," King Salman was quoted as saying in the letter.

"This letter has no legal basis to justify any action," Al Thani said in an interview with Al Jazeera.

"It's unfortunate that they see this as destabilisation because Qatar does not represent a threat to Saudi," he said.

Agencies