China's insurance regulator is opposed to multi-billion dollar bids by financial conglomerate Anbang for Starwood Hotels and a stable of properties owned by hedge fund Blackstone, according to respected business magazine Caixin.

Anbang has offered nearly $13 billion for Starwood, owner of the Sheraton and Westin brands, as well as $6.5 billion for the purchase of 16 luxury hotels from Blackstone.

But another US hotel giant Marriott International, which had already agreed to take over rival Starwood before the Anbang move, now looks likely to win that deal after hiking its offer by more than $1 billion this week to $13.6 billion.

The China Insurance Regulatory Commission is against both of Anbang's proposed acquisitions under rules which reportedly ban insurers from investing more than 15 percent of their assets overseas, Caixin quoted a source as saying.

The regulator also had a "disapproving attitude" towards the deals, the magazine said in a report on its website late Tuesday, but gave no other reasons.

The government agency and Anbang could not be reached for comment on Wednesday.

Anbang, which started as a property insurance firm before expanding into other financial services, has assets of 1.65 trillion yuan ($254 billion), according to its website.

The company has aggressively invested overseas through a string of deals. In November, Anbang bought US insurer Fidelity & Guaranty Life for $1.6 billion, after snapping up Korean insurer Tong Yang Life for around $950 million and Dutch insurer Vivat for about $167 million earlier in the year.

It bought New York's historic Waldorf Astoria hotel in 2014, but analysts question why a Chinese insurance company wants to become an international hotelier.