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Shares of troubled Canadian drug company Valeant Pharmaceuticals rose on the support of a key shareholder.

Shares fell 35% over the last week following a report questioning Valeant's relationship with a speciality pharmacy.

Hedge fund owner Bill Ackman said he has swept up 2 million shares as their price fell.

Mr Ackman - Valeant's second largest investor - already owned 19.5 million shares.

His company Pershing Square announced it will hold a call with the hedge fund's investors on Friday to discuss its continued investment.

On Monday Valeant also held a conference call with its investors to address claims raised in the report published by Citron Research, a short-seller and financial research company.

compared Valeant to Enron - which eventually became bankrupt in 2001, after auditing deceptions were discovered.

Citron suggested that Valeant's "unsavory business" included questionable distribution of its medicines, including selling to "phantom" buyers to show higher demand for its products:

"Citron believes the whole thing is a fraud to create invoices to deceive the auditors and book revenue," it wrote.

Valeant said it was setting up a committee to investigate the allegations.

The company also said it was asking the US Securities and Exchange Commission (SEC) to look into Citron and its intentions.

Valeant's chief executive Mike Pearson said the head of Citron, "intentionally designed the report to frighten our shareholders to drive down the price of our stock so he could make money for his short-selling."

Valeant purchased a $100m option to buy speciality pharmacy Philidor in December 2014.

Speciality pharmacies focus on difficult-to-store or dispense medication or medical devices. They can allow companies to get around the complex insurance system in the US.

Valeant is accused of using its relationship with Philidor to raise the prices of medications.

Valeant also confirmed that US prosecutors are investigating the relationship between its subsidiary Bausch & Lomb and doctors.

Valeant employs 18,000 people worldwide and reported full year revenues of $8.25bn in 2014.