ULAN BATOR, June 8 (Xinhua) -- Mongolia's two former prime ministers held in custody since April over corruption allegations were released on bail, judicial authorities said Friday.

Sanjaa Bayar and Chimed Saikhanbileg were released for health reasons. Three different district courts in the Mongolian capital jointly made the decision at the prosecutor's request.

The two former prime ministers are allegedly implicated in a large mining deal involving foreign investment. The court has also banned them from leaving the country.

The Independent Agency Against Corruption, Mongolia's top anti-corruption body, is investigating the Oyu Tolgoi copper-gold mine deal between the Mongolian government and the Anglo-Australian mining giant Rio Tinto. The deal was signed in 2009 during Bayar's term, with its financing arrangement revised in 2015 during Saikhanbileg's term.

The Oyu Tolgoi mine, located in a gobi desert 80 km north of Mongolia's border with China, is expected to produce 430,000 tons of copper and 425,000 ounces (about 12,050 kg) of gold annually for 20 years.