U.S. President Donald Trump said on Wednesday that he had noticed some signs of activity at Iran's Pickaxe underground nuclear facility and warned Tehran to be careful and not to play games, or the United States would hit the site hard.

The Pickaxe site is near Iran's heavily damaged Natanz uranium enrichment facility and contains two deeply buried tunnel complexes. Trump has repeatedly threatened since July to bomb the facility, according to ETNet.

Trump also said oil prices, which have risen because of the U.S.-Iran war, are unlikely to fall before the midterm elections.