Corus employs 24,000 people in the UK

Confirming media reports from the end of last month, CSN said joining the two businesses would make "compelling strategic and industrial logic".

CSN's informal offer is higher than Indian firm Tata Steel's existing �4.1bn formal bid for Corus, which has been accepted by the Corus board.

Tata's offer still requires backing from Corus shareholders.

In a statement Corus said it had received an approach and "a further announcement will be made in due course".

'Global powerhouse'

"A combination of CSN and Corus would create a global powerhouse with market leading positions and exceptional distribution networks across both developed and emerging markets," said CSN chairman and chief executive Benjamin Steinbruch.

Earlier reports had valued Tata's approach at �4.3bn, however this offer would be diluted by the inclusion of share options.

Without stock options, the CSN proposal values each Corus share at 475 pence, while Tata's offer is equivalent to 455p a share, or �4.1bn.

However, Tata has reserved the right to come back with a higher bid.

All change

The latest development is a distinct turnaround from the situation in 2002, when Corus made a �2.7bn bid for CSN.

The steel group later pulled out when its financial performance started to deteriorate.

CSN describes itself as one of the largest steel firms in Latin America, employing 8,000 people.

It has overseas operations in the US and Portugal.

Corus employs 47,300 people worldwide, including 24,000 in the UK at plants at Port Talbot, Scunthorpe and Rotherham.

It was formed out of the 1999 merger of British Steel and Dutch group Hoogovens.