Defense chief says US responded to 'credible threat' by Iran

The acting defense secretary tweeted that he approved the movement Sunday of the USS Abraham Lincoln carrier strike group as "a prudent repositioning of assets in response to indications of a credible threat by Iranian regime forces."

"We call on the Iranian regime to cease all provocation. We will hold the Iranian regime accountable for any attack on US forces or our interests," he said.

US officials have not specified the nature of the alleged threat from Iran, which has come under mounting pressure from President Donald Trump's administration.