The verdict leaves it to the government to decide the outcome of the battle for control of one of the last independent stock market operators in northern Europe, which began when Euronext made a first, unsolicited move in December.

The Norwegian bourse's response was to seek new bidders, encouraging U.S.-based Nasdaq to make a rival offer. Both bids are now set at 158 Norwegian crowns per share, valuing Oslo Bors at around 6.8 billion crowns (£606 million).

"We can confirm that we've received the advice, and that both Euronext and Nasdaq were found fit and proper," a finance ministry spokeswoman said on Monday.

The ministry has until May 14 to issue a ruling, although the deadline could be extended by a further 20 working days if it requires additional information, she added.

Earlier this month, Euronext said it had secured the backing of the holders of 53.1 percent of the shares in Oslo Bors, giving it a lead over Nasdaq, which has backing from about one third of the owners.

The Norwegian government has so far declined to say whether it will demand that any buyer meet a higher ownership threshold - such as a two-thirds majority - in order to prevent a minority owner from blocking changes in company bylaws.

If a bid is made conditional on owning significantly more than 50 percent, it could further complicate the takeover attempts.

"Euronext is convinced it is the best owner for Oslo Bors VPS, and welcomes the positive recommendation of the Norwegian financial supervisory authority to the Ministry of Finance," Euronext CEO Stéphane Boujnah said in a statement on Monday.

The operator of stock markets in Paris, Amsterdam, Brussels, Dublin and Lisbon said it directly holds 8.1 percent of the shares in Oslo Bors and other shareholders have irrevocably pre-committed or tendered 45 percent of the shares.

The Oslo Bors board, and its largest shareholders DNB and pension fund KLP which own 20 percent and 10 percent stakes respectively, continue to back the Nasdaq offer.

"We are pleased to be have been deemed fit and proper by the Norwegian Financial Supervisory Authority," said a Nasdaq spokesman.

Euronext shares were up 1.6 percent in early session trading in Paris.

(Writing by Sudip Kar-Gupta and Gwladys Fouche, Editing by Sherry Jacob-Phillips and Kirsten Donovan)

By Sudip Kar-Gupta and Terje Solsvik