In early morning deals, Glencore shares tumbled 3.70 percent to 369.8 pence and Xstrata sank 2.35 percent to 917.1 pence on London’s FTSE 100 index of top companies, which was 0.52 percent lower.

The Financial Times, which did not reveal its source, said Norges Bank Investment Management, the manager behind Norway’s oil-backed sovereign wealth fund, had “privately indicated” its opposition to the current terms of the Glencore-Xstrata merger.

In recent weeks, NBIM bought more than $500 million of Xstrata stock, taking its total stake to 2.97 percent, according to the daily business newspaper which cited regulatory filings.

Qatar Holding is one of Xstrata’s largest shareholders and has built up a stake of around 12 percent, the paper added.

Xstrata shareholders will vote on the mammoth merger deal on September 7 at an extraordinary general meeting in Zug, Switzerland.

Back in February, Glencore and Xstrata formalised a highly anticipated deal to create a raw materials behemoth.

Glencore is offering 2.8 of its shares per Xstrata share. However, Qatar Holding said in June that an exchange ratio of 3.25 Glencore shares “would provide a more appropriate distribution of benefits of the merger whilst properly recognising the intrinsic stand-alone value of Xstrata.”