President Donald Trump waded into a rapidly escalating Gulf crisis Tuesday, suggesting ally Qatar -- home to the largest US military base in the Middle East -- is funding extremism as he tacitly backed a diplomatic blockade of the emirate.

"So good to see the Saudi Arabia visit with the King and 50 countries already paying off," Trump said in a morning tweet.

"They said they would take a hard line on funding... extremism, and all reference was pointing to Qatar. Perhaps this will be the beginning of the end to the horror of terrorism!"