Brazil’s Camargo Correa Group must present a counterbid to take over  Cimpor or withdraw its merger proposal, Portugal’s stock market regulator (CMVM) told the company on Saturday.

On Wednesday Camargo Correa offered to merge its cement business with Cimpor and buy a stake of between 15 and 25 per cent in Portugal’s largest cement maker.

Cimpor is the target of a takeover offer by Brazil’s CSN.

CMVM said in a statement it "notified Camargo Correa that it started an administrative process with the purpose of making the latter comply its proposed merger with the rules on counterbids ... or withdraw it."

It said Camargo has 10 days to reply to the demand.

A counterbid has to target at least the same stake as in the initial takeover bid and be at least two per cent higher than the initial offer under CMVM rules.