Republican presidential nominee Donald Trump's increasingly hostile rhetoric toward his Democratic counterpart, Hillary Clinton, reached a new level of intensity Monday when he called Clinton "the devil" during a campaign rally in Pennsylvania.

The insult came as Trump blasted Sen. Bernie Sanders for endorsing Clinton after losing a heated primary fight for the Democratic nomination.

"If he would have just not done anything — just go home, go to sleep, relax — he would have been a hero," Trump said at the rally in Mechanicsburg. "But he made a deal with the devil. She's the devil."

It was not the first time Trump had described Sanders' endorsement of Clinton as a deal with the devil. At rallies in Iowa and Colorado last week, the Republican nominee accused Sanders of "selling out to the devil" and said he "sold his soul to the devil," CNN reported.

But according to The Associated Press, Monday's rally marked the first time in which he went so far as to call Clinton herself the devil.

Trump's comments came as he spent Monday staving off increased criticism over his war of words with the Gold Star family of Capt. Humayun Khan, a Bronze Star hero killed in the Iraq War. Republican leaders and veterans groups slammed Trump over the back and forth with the family, which began after Khan's father delivered a powerful speech last week at the Democratic National Convention.

Watch Trump's Monday comments below:

