In pursuit of acquiring mobile player Hutch-Essar, UK-based telecom giant Vodafone on Thursday offered to align with Ruias' Essar, saying it is the "natural partner" for the biggest acquisition deal in India.

"Essar (a 33 per cent stake-holder in HEL) is a natural partner. It is already there in the joint venture," Vodafone CEO Arun Sarin told reporters at the close of his two-day visit to India during which he met Cabinet ministers, including P Chidambaram and Dayanidhi Maran.

Keeping his options open to join  hands with other firms, Sarin said: "We are talking to several companies. We will see who we can have as partner on a long-term basis."

• Who is Arun Sarin?

Vodafone was the first player to announce its intention about acquiring Hutch-Essar and Sarin visited Hong Kong recently to meet officials of Hutchison Telecom (HTIL), which owns 67 per cent stake in HEL, before coming to India. Essar has also expressed its intention to buy HTIL's stake.

On reports that HEL could be valued up to $21 billion, Sarin made it clear that his company would not madly rush into a bidding war. "There is only a certain valuation to which we will go and not beyond," he said.

Stating that Vodafone, which started due diligence for HEL on Monday, would make its bid in the next few weeks for all "available equity," Sarin said he would come back in the next couple of weeks to pursue the matter but did not give a time frame for the deal.

Sarin said he was also open to partnership with other suitors, including Reliance Communications while listing out Vodafone's track record as "good partner."

The day also saw Reliance Communications chairman Anil Ambani visiting the national capital and calling on Finance Minister P Chidambaram and senior DoT officials.

He also met Maran and Telecom Secretary D S Mathur. Ambani's meeting comes just a day after Sarin and Essar chairman Shashi Ruia met Chidambaram and Maran on Wednesday. He, however, did not take any questions from the media.

His company started examining the books of Hutchison Essar Ltd for a possible bid, while Essar's bankers are already studying HEL's books.

While Vodafone has said it would complete due diligence of HEL in a couple of weeks, the company could face a downgrade in its credit rating by Standard and Poor's if its proposed bid for Hutch-Essar exceeds $19 billion.

British newspaper The Daily Telegraph quoted credit rating giant Standard & Poor's as saying that a "meaningful step-up" in Sarin's planned offer could cause it to cut its debt rating on Vodafone from 'A-' to 'BBB+' due to increase in cost of new borrowings.

It would be S&P's second downgrade in less than a year on Vodafone, reflecting rising debt levels and increased risk from the emerging markets it is moving into, the report said.

Vodafone already owns about 10 per cent stake in India's top mobile player Bharti and is seeking to sell this minority stake and buy a controlling stake in Hutch Essar.

S&P expected Vodafone to get around $2.3 billion for the Bharti stake, but a $19.3 billion bid for Hutchison Essar would increase net debt to around $48.3 billion, the report said.

The Daily Telegraph also quoted brokerage firm Exane BNP Paribas as saying it "failed to understand" how a bid valuing HEL at $17-18 billion could create value for Vodafone.

Hutchison Whampoa Director (Finance) Frank Sixt had last month said that a valuation below $14 billion would not excite the company.

With the company's valuation shooting through the roof, the interest of private equity firms' in the deal has started waning, the Financial Times had reported.

According to the report, private equity buy-out firms believe that they would not participate in any deal that valued Hutch-Essar much above $15 billion.

A small stake in Hutchison Essar was sold last year that valued the venture at $10 billion, while analysts last month estimated the company's enterprise value had risen to $14 billion.

Among the private equity groups in talks to join a Reliance-led bid for Hutchison Essar are Blackstone, KKR, Carlyle and Texas Pacific Group.

The report quoted an unnamed person with knowledge of the situation as saying: "Private equity groups will not play this game at $18 billion. That price is crazy, a joke."

• The race for Hutch-Essar: Complete coverage