US President Donald Trump has taken aim on Twitter at his one-time ally senator Bob Corker with a series of derisive posts blaming the Republican for the Iran nuclear deal while alleging he "begged" him for endorsement and wanted to be secretary of state.

Key points: Mr Trump says he ditched running for Senate after "begging" him for endorsement

Mr Trump says he ditched running for Senate after "begging" him for endorsement Mr Corker says "it's a shame the White House has become an adult day care centre"

Mr Corker says "it's a shame the White House has become an adult day care centre" Mr Corker, a former ally, had a falling out with Mr Trump after the Charlottesville rally

Mr Corker, who announced his retirement from the Senate last month, responded to Mr Trump with a sarcastic Twitter post of his own.

The senator from Tennessee had been considered by Mr Trump for the secretary of state position in the months after Mr Trump's November 8 election win.

Mr Corker, chairman of the Senate Foreign Relations Committee, has been more critical of Mr Trump in recent months, including over the handling of an August white supremacist demonstration in Charlottesville in Virginia.

"Senator Bob Corker "begged" me to endorse him for re-election in Tennessee. I said "NO" and he dropped out [said he could not win without my endorsement]," Mr Trump wrote.

"He also wanted to be Secretary of State, I said "NO THANKS." He is also largely responsible for the horrendous Iran Deal!

"Hence, I would fully expect Corker to be a negative voice and stand in the way of our great agenda. Didn't have the guts to run!"

Mr Trump has long criticised the 2015 international nuclear pact, a signature foreign policy achievement of former president Barack Obama in which Iran agreed to reduce its nuclear program in exchange for easing of sanctions.

Mr Corker, whose retirement is a blow to the Republican Party struggling to balance divisions between mainstream and more populist wings, hit back in a tweet on Sunday.

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In an interview with the New York Times, Mr Corker said the President was treating his office like "a reality show" and his threats to other countries could put the US "on the path to World War III".

Mr Corker said in conversations this year Mr Trump repeatedly indicated he wanted to attend a rally in Tennessee on his behalf and last week phoned him in an attempt to talk him out of retiring.

"When I told him that that just wasn't in the cards, he said, 'You know if you run, I'll endorse you'," Mr Corker said.

"I said, 'Mr President, it's just not in the cards; I've already made a decision'. So then we began talking about other candidates that were running."

Last week, asked about reported tensions between Mr Trump and the person he eventually chose to be secretary of state, Rex Tillerson, Mr Corker's response was seen as a jab at Mr Trump.

"I think Secretary Tillerson, Secretary [of Defence James] Mattis, and Chief of Staff [John] Kelly are those people that help separate our country from chaos," Mr Corker said, referring to Defence Secretary James Mattis and White House chief of staff John Kelly.

Mr Corker also said Mr Tillerson was "in an incredibly frustrating place" where he "ends up not being supported in the way that I hope a secretary of state would be supported", according to media reports.

Later on Sunday, Mr Trump directed another tweet at Mr Corker, suggesting the Iran deal was his only achievement and that he was not a politician that could get things done.

"Corker gave us the Iran Deal, & that's about it. We need HealthCare, we need Tax Cuts/Reform, we need people that can get the job done!" he wrote.

But it was not the first time Mr Trump has tweeted about his former Republican ally while attacking his alleged shortcomings as a politician.

In August, Mr Trump said Mr Corker was "constantly asking me whether or not he should run again in '18" — that was after the senator's remarks on Mr Trump's response to the Charlottesville demonstration.

At the time, Mr Corker had said that "the President has not yet been able to demonstrate the stability, nor some of the competence, that he needs to demonstrate in order to be successful".

White nationalists and counter-protesters clash in Charlottesville on August 12. ( Reuters: Joshua Roberts )

Reuters