Facing a tough re-election battle, US President Donald Trump has replaced his campaign manager.

Mr Trump said he had substituted Bill Stepien, a field director for his 2016 campaign, in place of Brad Parscale.

Mr Parscale - who was reportedly blamed by Mr Trump's inner circle for a poorly attended rally in Oklahoma last month - will stay on as senior adviser.

Opinion polls show the president is trailing his Democratic challenger Joe Biden ahead of November's election.

Mr Trump's statement on Facebook on Wednesday evening said: "Brad Parscale, who has been with me for a very long time and has led our tremendous digital and data strategies, will remain in that role, while being a Senior Advisor to the campaign."

Mr Parscale is said to have found himself sidelined in recent weeks after the president's comeback rally in Tulsa flopped.

Mr Trump's daughter Ivanka Trump and her husband Jared Kushner, both White House advisers, are reported to have blamed Mr Parscale for the debacle.

Mr Parscale had boasted that more than one million people registered to attend, but fewer than 6,200 showed up at the arena, the local fire department said.

After the rally, Mr Parscale went on Twitter to blame a blocked security gate, protesters and the media for the disappointing turnout.

His role as a Trump strategist has apparently proved lucrative for the 44-year-old, who last year reportedly bought a $2.4m waterside mansion in Fort Lauderdale, Florida.

Mr Parscale, a brash figure who served as a warm-up act for Mr Trump at rallies, was appointed campaign manager in February 2018.

The BBC's US partner CBS News reported recently that Mr Parscale did not even vote in the 2016 election, citing his difficulty in obtaining a postal ballot while working at Trump Tower in New York City.

He was Mr Trump's fourth campaign manager, following Kellyanne Conway, Paul Manafort and Corey Lewandowski.

His replacement, Mr Stepien, was a former aide to ex-New Jersey Governor Chris Christie.

Mr Stepien's name came up in the so-called Bridgegate scandal that was widely perceived to have scuppered Mr Christie's presidential ambitions.