Qatar Airways exploited the post-Brexit slump in shares at British Airways owner IAG to increase its shareholding to 20 percent, the Gulf carrier announced on Monday.

In a statement, Qatar Airways boss Akbar Al-Baker said his company had raised its 15.01 percent stake to 20.01 percent because of the current state of the market.

"The recent market valuation of one of the world's leading airline groups has provided what we believe is an attractive opportunity to increase our shareholding in IAG," said Baker.

The move was also announced by Qatar Airways on social media.

"News alert: Qatar Airways now holds a 20% stake in International Airlines Group (IAG)," the Doha-based carrier said on Twitter.

It is the fourth time in just three months Qatar has upped its holding in IAG and comes after shares in the company fell following the Brexit vote by the UK to leave the European Union.

IAG shares have fallen by more than 20 percent since the vote on June 23.

There is currently a cap on non-EU shareholders of IAG meaning international investors cannot own more than 49 percent of a European airline.