LONDON (Reuters) - Anglo American does not consider a proposed $39 billion takeover offer from BHP Group ( BHP ) as attractive, two sources told Reuters, as some large investors dismissed it as opportunistic.

BHP on Thursday offered Anglo's shareholders 25.08 pounds ($31.39) per share, or $38.8 billion, a premium of 31% to the market close on Wednesday. It would take over Anglo after a spin-off of two assets.

Speaking on condition of anonymity because the matter is private, one of the sources said the offer did not address the complexities of demerging the Anglo American Platinum and Kumba Iron Ore businesses in South Africa.

BHP has until May 22 to come back with a binding bid, but Anglo's board will give a formal response in the coming days.

For now, Anglo, which has a market value of $36.7 billion, said it would be reviewing the offer, without elaborating.

The proposed tie-up would create a group with around one tenth of the global output of copper, which is in demand for its use in electric vehicles and new technologies, such as automation and artificial intelligence.

BHP has made the offer as the company continues a strategic review of its assets started in February in response to a 94% fall in annual profit and a series of writedowns caused by to lower commodity demand.

One of the source said Anglo American's management was continuing "full steam ahead" with the review.