Donald Trump proclaimed himself the "law and order candidate" Monday, emphasizing increased threats to police and declaring only he can keep Americans safe in a nation reeling from gun violence.

"I am the law and order candidate," the Republican party's presumptive presidential nominee said in a speech in Virginia Beach, Virginia.

The declaration, reminiscent of remarks made by former president Richard Nixon, came as Trump highlighted recent killings including the horrific shooting deaths of five Dallas officers in a gunman's sniper-like assault.

"The attack on our Dallas police is an attack on our country. Our whole nation is in mourning," Trump said, as he pledged to "fight" for law enforcement personnel and ensure they have Washington's full backing.

"Without safety we have nothing."

Trump, who veered from his speech on veterans issues to discuss the violence, also stressed that he is the candidate of compassion.

"But you can't have true compassion without providing safety for the citizens of our country," Trump said.

The billionaire political neophyte's reaction to the latest US events has been closely scrutinized in recent days.

Often quick to lash out on Twitter or offer scathing critiques, Trump has largely steered clear of aggressive criticism after the deaths of two black men last week at the hands of police officers.

He halted his campaigning for a day after Thursday's Dallas police murders, as did his Democratic rival Hillary Clinton.

But on Monday Trump insisted he was uniquely prepared to back the nation's police forces, and hammered Clinton as "weak, ineffective" and pandering.

"America's police and law enforcement personnel are what separates civilization from total chaos and the destruction of our country as we know it," Trump said.

New Jersey Governor Chris Christie, a former 2016 presidential candidate and a potential Trump running mate, was on board with Trump's message.

"We need a president who once again puts law and order at the top of the priority of the presidency of this country," Christie told the crowd shortly before Trump spoke.

Trump's declaration echoed the pronouncements of former president Richard Nixon, who as a candidate declared he would be tough on crime.

"I pledge to you, we shall have order in the United States," Nixon said in a 1968 campaign ad.