Canadian chemical company Canexus Corp (CUS.TO) said Canada's antitrust regulator had approved its proposed buyout by rival Superior Plus Corp (SPB.TO).

This comes a day after the U.S. antitrust regulator filed a complaint to block the deal, saying the companies were two of the three manufacturers of a chemical needed to whiten wood pulp for paper production.

Alberta-based Canexus also said on Tuesday that it was in talks with Superior Plus to potentially extend the closure of the deal to allow the Toronto-based company to litigate the action by the U.S. Federal Trade Commission.

When the companies announced the $324 million deal in October last year, they said the transaction was expected to close on June 29.

Up to Monday's close, Canexus shares had fallen about 11 per cent in the past 12 months, while Superior Plus shares had fallen 20 per cent.