Grieving actress Michelle Williams has returned to work on a film set just yards from where her former fiance Heath Ledger was found dead.

The 27-year-old filmed scenes for her new film Mammoth on set in Manhattan, New York, on Monday.

The former Dawson's Creek star was shooting the scenes for the upcoming picture in Sweden when she heard of her former lover's death last month.

But Williams' friends fear she has returned to work too soon after Ledger's funeral in Australia on Saturday.

A source tells the New York Post, "She looked heartbroken but did a good job keeping her composure. She was also bleary-eyed, but she had a job to do, and she did it."

Ledger was found dead in his New York apartment on January 22, aged just 28. Toxicology results released on Wednesday revealed he was killed by an accidental overdose of prescribed medications.