With an increase in its stake in Australia's Riversdale Mining, Tata Steel is made it tougher for the miner Rio Tinto to close its $3.9 billion bid for this company. Riversdale Mining's main focus is coal mining in Mozambique in its Benga and Zambeze projects there.

Tata Steel raised its stake in Riversdale from 24.2% to 27.1% spending $101 million. Tata Steel is already biggest stake holder in the company. Riversdale has Brazil based CSN as its second largest stakeholder with 19.9%.

Now with Tata's raise in stake, it has become more the difficult for the Rio to go ahead in bidding process. Shares of the Riversdale also fell, which points to the market sentiment about the deal.

Rio has demanded 50.1% acceptance, which now seems too difficult to get. As with Tata's move, it now needs almost 100% acceptance from individual shareholders.

Tata Steel's move was a surprise, as its last month only when company said that it will decide whether to sell or keep stake. Now Rio has two options, reduce its acceptance from 50.1% to the amount it believes it can persuade, second deal with Tata or CSN.