Ratings agency Standard & Poor's said on Wednesday it would likely raise its rating on commodities giant Glencore if its proposed merger with mining company Xstrata goes ahead.

Glencore's BBB long-term status is under review following the $61.9 billion deal announced on Tuesday, S&P said in a statement.

"If and when Xstrata shareholders approve the merger and antitrust authorities give their green light, we expect to assign a 'BBB+' rating to the enlarged entity," it said.

The decision will however depend on further assessment of the joint group's capital spending plans and strategy. Xstrata already has a BBB+ rating.

The merger of the two Swiss-based groups would create a company with revenues of about $209 billion and put it among the world's top mining groups, behind BHP Billiton, Vale and Rio Tinto.