A federal judge in Texas has dismissed Walmart Inc's lawsuit against the US government where the retailer was seeking clarity over the responsibilities of pharmacists in filling opioid prescriptions.

Walmart said on Friday it will appeal.

In a decision on Thursday night, US District Judge Sean Jordan said the government had not waived its sovereign immunity from being sued. The judge said that as a result, he lacked jurisdiction over the case.

Jordan's decision came six weeks after the government filed its own lawsuit accusing Walmart of fueling the US opioid epidemic by having ignored warning signs from its pharmacists and filled thousands of invalid prescriptions.