DES MOINES, Iowa — Republican presidential nominee Donald Trump Sunday cast aside his running mate’s suggestion that the U.S. should be ready to strike Syrian targets to protect civilians caught in the country’s escalating humanitarian crisis.

The comment was yet another illustration of Republican vice presidential nominee Mike Pence’s challenge as he attempts to validate the GOP nominee’s unusually vague positions on international diplomatic and military affairs.

“He and I haven’t spoken, and I disagree. I disagree,” Trump said during his debate with Democratic nominee Hillary Clinton Sunday.

Trump was referring to Indiana Gov. Mike Pence’s suggestion made five days earlier during the vice presidential candidates’ debate that the U.S. be ready to use force to keep Russian-backed Syrian forces from killing civilians in Aleppo, a city caught in the five-year-long civil war. Trump has advocated a hands-off approach to dealing with the regime of Syrian President Bashar al Assad.

“If Russia chooses to be involved and continue, I should say, to be involved in this barbaric attack on civilians in Aleppo, the United States of America should be prepared to use military force to strike military targets of the Assad regime to prevent them,” Pence said during the debate with Virginia Sen. Tim Kaine on Tuesday.

On Sunday, Trump did not suggest a different plan for dealing with Aleppo. He instead restated his support for creating so-called safe zones for Syrian refugees, to be paid for by Arab nations, and his primary Middle Eastern focus, eradicating the Islamic State terrorist group in the region.

“We have to worry about ISIS before we can get too much more involved,” he said.

The difference underscores Pence’s superior fluency on such issues, as a former 10-year member of the House Foreign Affairs Committee as a U.S. representative from Indiana.

Pence’s campaign did not reply to a request for comment by The Associated Press on Trump’s disagreement with Pence’s statement.