Police have deployed gas to disperse crowds in Phoenix, Arizona, after protesters outside a rally by US President Donald Trump threw rocks and bottles at officers.

“People in the crowd have begun throwing rocks and bottles at police. They also dispersed some gas in the area,” Phoenix Police Department spokesman Sergeant Jonathan Howard said.

“Police have responded with pepper balls and OC (oleoresin capsicum) spray in an attempt to disperse the crowd and stop the assaults.”

During the speech, Mr Trump blamed the media for the condemnation of his response to a violent rally organised by white supremacists, which led to the killing of a counter-protester.

Police use tear gas to break up protesters. Photo: AFP

The US president opened his political rally in Phoenix with a call for unity, saying: “What happened in Charlottesville strikes at the core of America and tonight, this entire arena stands united in forceful condemnation of the thugs that perpetrated hatred and violence.”

But he quickly trained his ire on the media, shouting that he “openly called for healing unity and love” in the immediate aftermath of Charlottesville and claiming the media had misrepresented him.

He read from his three responses to the violence − getting more animated with each one.

Democrats and fellow Republicans had denounced Trump for placing blame for the Charlottesville violence on “both sides”.

President Donald Trump reacts to the crowd at a rally at the Phoenix Convention Center. Photo: Getty

Trump omitted that part of his reaction from his recap Tuesday night.

“You know where my heart is,” Trump said. “I’m only doing this to show you how damned dishonest these people are.”

After the rally, a day of noisy but largely peaceful protests outside the Phoenix convention centre turned unruly as police fired pepper spray at crowds after someone lobbed rocks and bottles at officers.

Trump spoke after Vice President Mike Pence and others called repeatedly for unity.

In the comfort of his most fervent fans, Trump often resurrects his free-wheeling 2016 campaign style, pinging insults at perceived enemies such as the media and meandering from topic to topic without a clear theme.

Although Trump’s high-profile warm-up acts suggested the president’s speech would be about unity, the president was more intent on settling scores.

Trump began his Arizona visit with a brief trip to the southern edge of the country.

While touring a Marine Corps base in Yuma that is a hub of operations for the US Border Patrol, Trump inspected a drone and other border equipment on display in a hangar.

Afterward, he spent about 20 minutes greeting service members in the gruelling, 41 degree heat, signing caps with his “Make America Great Again” campaign slogan and posing for selfies on the tarmac just steps from Air Force One.

– RAW