Washington (CNN) President Donald Trump on Wednesday escalated his political fight with California by threatening to have the Environmental Protection Agency pursue action against San Francisco for its homelessness problem.

"It's a terrible situation that's in Los Angeles and in San Francisco," Trump said of homelessness to reporters aboard Air Force One, according to a pool report. "And we're going to be giving San Francisco -- they're in total violation -- we're going to be giving them a notice very soon."

"EPA is going to be putting out a notice," he added. "They're in serious violation."

He said pollution was flowing into the ocean because of waste in storm sewers, specifically citing used needles, though he did not provide details or evidence, and it's unclear on what grounds the city would be in violation of EPA regulations.

Asked by a reporter on Thursday about Trump's comments, EPA Administrator Andrew Wheeler said he had staff looking into the issue as recently as last week and that the agency is "taking a look at whether or not permits have been in violation."