UK mining giant Anglo American has rejected its rival BHP’s plea to extend the looming deadline for a final offer on a proposed £39bn merger.

Earlier on Wednesday, Australian BHP attempted to ease concerns about its plans for Anglo American’s business in South Africa ahead of elections in the country.

It made commitments that included job security for employees there, but said it needed an extension on talks “to allow further engagement” on the plans.

However, Anglo’s decision means the mega-merger is in jeopardy unless BHP changes its offer before 17:00 on Wednesday.

The pair have been wrangling over the deal since Anglo American rejected BHP’s first takeover approach, a £31.1bn offer, at the end of April.

Anglo then rejected BHP’s second £34bn offer at the start of May and its third offer of £38.6bn last week, but some Anglo shareholders urged the company to keep negotiating.

Anglo and the South African government have also cited concerns about BHP’s proposal to spin off the South African businesses.

After rejecting BHP the third time, Anglo announced its own plans to break up its business by selling or spinning off major parts of the firm including its De Beers diamond operation and its platinum division, with a view to focusing on key areas such as copper, premium iron ore and crop nutrients.

BHP has made a series of proposals it said it would keep for at least three years to ease Anglo’s concerns.

These include maintaining current staff levels at Anglo’s Johannesburg office, keeping BHP listed on the Johannesburg Stock Exchange, and sharing the cost of increased South African employee ownership “if required to secure regulatory approvals”.

However, Anglo said that BHP’s offer still includes “the same highly complex and unattractive structure as the proposals previously rejected on 26 April 2024 and 13 May 2024”.

Speaking to the BBC’s Today programme on Wednesday before Anglo’s update, Ben Davis, head of mining at analyst Liberium Capital, said there was “not really much meat on the bones” of BHP’s proposals.

He added that they amount to a continuation of its commitment to South Africa rather than an improvement.

He also expressed sadness about the prospect of another listed UK company being snapped up by an overseas business.

“To see [Anglo American] gone from the London Stock Exchange would certainly be a loss,” he said.