US Republican presidential candidate Donald Trump has said he would crack down on immigrants who overstay their visas.

In a campaign speech in Des Moines, Iowa, Mr Trump also cited the shooting death of a cousin of NBA player Dwyane Wade to urge African-American voters to rally behind him, calling it an example of violence that has to be addressed.

Mr Trump sought to clarify his views on how to overhaul the US immigration system after saying earlier in the week that he was softening on his plan to deport all 11 million illegal immigrants.

That stance drew criticism from conservatives who wanted him to stand fast after he won the Republican presidential nomination in large part by a hardline stance that would include building a wall along the US border with Mexico.

In his speech, Mr Trump said he would seek to institute a tracking system to ensure illegal immigrants who overstay their visas are quickly removed.

He said he would also propose an e-verify system to prevent the illegal community from gaining access to welfare and other benefits.

"If we don't enforce visa expiration dates, then we have an open border - it's as simple as that," he said.

In outlining his views, Mr Trump said addressing illegal immigration is important to helping Americans find jobs.

"Every time an African-American citizen, or any citizen, loses their job to an illegal immigrant, the rights of that American citizen have been violated," he said.

"Equal protection under the law must include the consistent application of our immigration laws."

Mr Trump said his first priority upon taking office next January would be the immediate deportation of thousands of illegal immigrants who remain in the United States despite having committed crimes.

"These international gangs and cartels will be a thing of the past. Their reign of terror will be over. In this task, we will always err on the side of protecting the American people - we will use immigration law to prevent crimes, and will not wait until some innocent American has been harmed or killed before taking action," he said.

He did not explain how his plan would affect many of the illegal community who have been in the United States for decades and obeyed US laws.

Mr Trump said the death in Chicago of Wade’s cousin Nykea Aldridge, 32, was an example of turmoil in US inner cities.

Ms Aldridge, a mother-of-four, was killed as she pushed her child in a buggy on Chicago’s south side on Friday.

Police believe the shooting followed a dispute between a number of men and Ms Aldridge was an innocent bystander caught in the crossfire. Her child was not injured.

The incident permitted Mr Trump to bring up again his desire to be a "law and order" president and underscore his drive to appeal to African-American voters who traditionally vote Democratic.

"It breaks all of our hearts to see it, it's horrible," Mr Trump said. "And it's only getting worse. This shouldn't happen in our country. This shouldn't happen in America. We send our thoughts and our prayers to the family, and we also promise to fight for a much, much better tomorrow."

Mr Trump raised the subject after sending out tweets earlier in the day that prompted charges of insensitivity to the death and accusations he sought to exploit it for political purposes.

Mr Trump is running neck and neck with Democratic candidate Hillary Clinton in polls in the state with 72 days until the 8 November election. 

The New York businessman was the headline speaker at "Joni Ernst's Roast and Ride," a charity event for military veterans run by US Senator Joni Ernst, a Republican.

Meanwhile, Mrs Clinton received her first national security briefing since accepting her party's nomination for the presidency last month.
Mrs Clinton, a former secretary of state, attended the meeting alone, according to a pool report.
The meeting was held at the Federal Bureau of Investigation's field office in White Plains, New York, not far from the Chappaqua, New York, residence she shares with her husband, former president Bill Clinton.

It lasted a little over two hours.
Mr Trump, recently received his first briefing, as well.