Mittal Steel, owned by Indian tycoon Lakshmi Mittal, has launched its bid for French rival Arcelor, after the go-ahead from European regulators.
Arcelor says it has not exhausted options yet to fend off the bid
France, Belgium and the Luxembourg have given the approval for Mittal's 19.2bn euro ($24.6bn; £13.02bn) hostile takeover bid for steel firm Arcelor.
Luxembourg-based Arcelor has repeatedly voiced its opposition to the bid.
Earlier in the week, Mr Mittal said shareholders would be able to decide on "the value and merits of our proposal".
This comes four months after the surprise takeover offer for Arcelor was originally made.
Arcelor's management has rejected the planned deal ever since it was first mooted on 26 January.
Mittal's offer is made up of three-quarters stock and one-quarter cash, including 547.6 million new Mittal shares.
HQ in Rotterdam/London
Steelmaking facilities in 16 countries
Customers in 120 countries
Shipped 49.2m tons in 2005
Revenues of $28.1bn in 2005
It has previously said it would consider "marginally" upping the offer - but made no reference to that in the bid launch.
In Luxembourg, Belgium and France, the offer will stand between May 18 and June 29.
In the US, the offer will open once the US financial watchdog, the Securities and Exchange Commission, has given the go-ahead for a registration statement, Mittal Steel said.
While US regulators and individual European states have cleared the deal on antitrust grounds, the firm is still waiting for EU-level regulatory approval.
The EU is set to approve the deal by June 7.
HQ in Luxembourg
Shipped 46m tons in 2005
Revenues of 32.6bn euros in 2005
Formed in 2002 by merger of European firms Arbed, Aceralia and Usinor
If the takeover is successful, it will create a global giant worth about $40bn employing 320,000 people and producing about 10% of the world's steel.
Arcelor's chairman Joseph Kinsch recently said the firm had not exhausted its options to prevent the takeover.
It has already promised an increased 2005 dividend and a 5bn euro share buyback at a price above the market level in order to convince sharholders not to accept the rival offer.