Through its affiliate, Ataer Holding, it has signed a provisional deal to buy British Steel after the UK steelmaker was forced into liquidation in May.

The Ankara-based fund hopes to complete the purchase by the end of 2019.

The fund, which is the largest of its kind in Turkey, has 362,968 members and revenue of $9.8 billion. Its total assets were worth $19.3 billion in 2018.

OYAK chairman Mehmet Tas is a former army general. The fund does not receive aid from the government and says it is not affiliated with any institution.

Set up in 2005, Ataer Holding is also the largest shareholder of Turkish steel group Erdemir, having bought a 49.3 percent stake in 2006, according to the fund's website.

The privatisation of Erdemir was seen as crucial to Turkey's economic recovery programme, supported by the International Monetary Fund.

Initially, a top court blocked the sale but Turkey's competition board overruled the judges in September 2006.

The fund's other businesses range from concrete and energy firms to financial services and the automotive sector.

Its most recent major acquisition was the Portuguese cement company Cimpor after a deal announced in October 2018.

It has faced some controversies, including strikes over higher pay in 2015 in Turkey's largest car plant, managed by Renault and OYAK in a joint venture dating back to 1969.

And in 2012, former OYAK chairman Yildirim Turker -- a retired lieutenant general -- was detained over links to the 1997 military coup.

Turker was among 21 suspects given a life sentence in April 2018 for their role in the coup, though none were jailed due to old age and health issues.