Officials with the United States military believe that the government of Iran gave its surrogates and proxy forces the go-ahead to attack U.S. forces.

Here's what we know

According to NBC News, which cited three U.S. officials familiar with the matter, an Iranian official talked about using groups backed by Iran to target American forces. These discussions were coupled with movement of Iranian-backed forces in the Middle East.

These groups include Yemen's Houthi rebels, who have attacked U.S. ships, and Shiite militia groups, trained by Iran, who have attacked U.S. forces in Iraq.

While U.S. Central Command declined to provide details, a spokesman told NBC News that "U.S. Central Command has seen recent and clear indications that Iranian and Iranian proxy forces were making preparations to possibly attack U.S. forces in the region." He added that this included "threats on land and in the maritime."

U.S. Central Command oversees military operations and partnerships in a region stretching from Egypt to Pakistan and north to Kazakhstan. It includes Iran, Iraq, Syria, and Yemen. The head of U.S. Central Command, Marine Corps Gen. Frank McKenzie, has requested additional troops in order to deal with the increased activity by Iranian-backed groups.

On Sunday night, White House national security adviser John Bolton announced that the U.S. would be deploying the USS Abraham Lincoln Carrier Strike Group and a bomber task force to the Middle East. Bolton said this would send Iran the "clear and unmistakable" message that any action on Iran's part would be met with "unrelenting force."

When this was announced, CBS News spoke about "chatter" that Iranian-backed Shia militias were attacking U.S. forces in Iraq.

NBC's sources said that the deployment of these forces had not changed Iran's support for its surrogates and proxies attacking American interests.