Having the first American black president was not enough to improve the lives of African-Americans in the United States, Republican presidential frontrunner Donald Trump pointed out over the weekend.

In fact, the real estate mogul said, these citizens have been living in worse conditions "than just about ever" during the administration of President Barack Obama.

"He [Obama] has done nothing for African-Americans. You look at what's gone on with their income levels. You look at what's gone on with their youth. I thought that he would be a great cheerleader for this country," Trump said.

"I thought he'd do a fabulous job for the African-American citizens of this country. He has done nothing," he told ABC's "This Week" that was aired on Sunday, according to Huffington Post.

Trump, who has been leading in all polls on the Republican presidential nomination race, blamed Obama for not lifting a finger about the community's problem in terms of unemployment.

"I think that he has set a very poor standard. I think he has set a very low bar and I think it's a shame for the African-American people," he added, according to CNN.

Trump made the statement in response to a question about a tweet he posted in 2014 in which he said Americans would not see another black president in the coming generations due to President Obama's poor performance.

The reality TV star, who was once sued by the Justice Department for allegedly discriminating against black tenants in his apartment complexes, is convinced he is the one who can win the black vote.

In the same interview, Trump complained that Republicans have only given him vicious attacks instead of a warm welcome ever since he entered the GOP's nominating process for presidential candidate in 2016 US presidential polls.

He said he has been on the defence against Republican presidential candidates ahead of the GOP's first presidential debate, which will be aired on Fox this week.

"I'm not looking to attack them. I didn't start the attacks, but I have been attacked and I counter punch. I mean, they attacked me first and I hit them back and maybe even harder than they hit me," Trump said.

"But the fact is that I've been attacked pretty viciously by some of these guys," he said in the same interview, according to The Hill.