Former boxing world champion Amir Khan and Liverpool's Paul Smith are backing a campaign to raise £500,000 to help investigate safety and welfare across combat sports.

The Liverpool-based Global Fighters' Association (GFA) says the investigation will examine fighters' medical care, pay, contracts and support after retirement.

The group campaigns for better working conditions for boxers and other combat sports says the inquiry, to be led by barrister Jonathan Caplan KC, will gather evidence from fighters, doctors, referees and promoters.

Smith, a former British champion, told BBC News many fighters struggled with high medical costs and low earnings, and needed better protection.

He said he had sometimes paid between £700 and £1,000 a year for medical tests during his career.

Smith said some boxers competing at lower levels could earn only a few hundred pounds after expenses, despite spending weeks preparing for a fight.

"We want to try and create some form of safety blanket for fighters," he said.

Smith also spoke about the difficulties of adjusting to life after boxing.

"You lose that purpose, you lose that identity, you lose your day-to-day routine," he said.

Khan, a co-founder of the GFA, said there needed to be an organisation fighters could turn to "when something goes wrong", whether during training, over contracts or after retirement.

The fundraising campaign will support the investigation and the GFA's wider plans to establish a trade union.

The British Boxing Board of Control, which regulates professional boxing in Britain, already requires annual medical examinations and brain scans.

Its general secretary, Robert Smith, told BBC Sport earlier this year that the board provided insurance for death and permanent injury. He also said it would support the creation of an independent fighters' union.