(Reuters) – The U.S. Food and Drug Administration on Tuesday sent warning letters to nine online networks operating a total of 53 websites to stop illegally marketing unapproved versions of opioid medications.

The regulator said http://bit.ly/2xLmrmB it is taking additional steps with these warning letters by going right to the source of the illegal supply of unapproved and misbranded versions of opioid drugs, including tramadol and oxycodone.

These steps by the regulator come at a time when the United States continues to grapple with an escalating opioid crisis. The regulator said a number of illegal and unapproved opioid medications are provided either by pharmacies or online websites.

“The internet is virtually awash in illegal narcotics,” FDA Commissioner Scott Gottlieb said in a statement.

Opioids were involved in more than 42,000 overdose deaths in 2016, the last year for which data was available, according to the U.S. Centers for Disease Control and Prevention.

“Drug dealers and rogue website operators are using the internet to fuel the opioid crisis,” Gottlieb added.

The regulator has requested responses from the nine companies within 10 working days, or they may be subject to product seizure or injunction.

(Reporting by Anuron Kumar Mitra in Bengaluru; Editing by Maju Samuel)