US President Donald Trump hailed America on its 250th birthday Saturday as the “crowning achievement” of human history, even as he used the event to renew his attack on domestic opponents he branded communists.

In a speech delayed by several hours when storms forced the temporary evacuation of crowds in Washington, Trump claimed that under his presidency the United States was “prouder than ever before.”

While Trump had promised a huge political rally to stamp his brand on the national celebrations, the 80-year-old Republican largely stuck to a more traditionally patriotic script.

“For two and a half centuries, our American republic has stood as the crowning achievement of human history,” Trump told tens of thousands of people on the National Mall.

On stage, he also hailed veterans from World War II and the Korean and Vietnam wars. But he then hailed the latter two as examples of the battle against “communists” — reprising his message from his speech on Friday night at the iconic Mount Rushmore monument.

“Our warriors did not fight communism on battlefields across the word, only to have that menace rear its ugly head right back here in America. We’re not going to let it happen,” he said.

Trump has repeatedly hammered home the theme recently ahead of November’s U.S. midterm elections, after the anti-establishment left of the Democratic Party won a string of US primary victories. “It’s like a cancer, you’ve got to cut it out,” he added.

The US leader also used the speech to boast of the recent military campaigns against Iran and Venezuela, saying Washington had “wiped out” Tehran’s military. (AFP)