U.S. Drug Enforcement Agency investigating Hayden Panettiere's death - report

U.S. Drug Enforcement Agency (DEA) officials are reportedly investigating Hayden Panettiere's death.

On Sunday, the Heroes actress was found unresponsive at an apartment in Greenville, South Carolina and was pronounced dead at the scene. She was 36.

At present, officers at the Greenville City Police Department are leading the investigation into Panettiere's sudden passing, but on Wednesday, journalists at ABC News reported that agents at the DEA are "assisting".

Representatives for the DEA and the Panettiere family have not yet commented on the update.

Previously, editors at TMZ claimed Naloxone - a drug that can be used to reverse an opioid overdose - was found at the apartment where the Nashville star died.

In a police report, the officer stated that Panettiere's on-again, off-again boyfriend Brian Hickerson and his brother, Zack Hickerson, were at the residence when emergency services arrived at the scene.

Meanwhile, tributes for the former child star continue to flow, with Jack Coleman posting an emotional message via Instagram on Wednesday in which he remembered his Heroes co-star.

Panettiere played cheerleader Claire Bennet on the superhero TV drama, while Coleman took on the role of her onscreen dad, Noah Bennet. The show ran for four seasons from 2006 until 2010.

"I've loved Hayden since day one of the pilot of Heroes, 20 years ago, when she introduced herself by shouting 'daddy' and throwing her arms around me. From that day on, she called me daddio. She was Haydini, because she was a magician," the actor wrote. "She brought joy to the set and a photographic memory. Everyone was in awe of her ability to bring it every take. A tiny colossus who loved to laugh. We laughed a lot. That shining face, that megawatt smile, that wasn't just for the camera. That was her. She glowed."