Republican presidential candidate Donald Trump has said that if abortions are made illegal in the US women who have them should be punished.

"There has to be some form of punishment," he said in a fierce exchange at a town-hall style event in Wisconsin on Wednesday.

Pressed by MSNBC's Chris Matthews on the nature of that punishment, Mr Trump responded: "I haven't determined what the punishment should be."

The property billionaire's comments provoked a torrent of condemnation.

Democratic White House front runner Hillary Clinton pounced on Twitter, saying: "Just when you thought it couldn't get worse. Horrific and telling."

His campaign later issued a statement saying the abortion issue should be left to individual US states to determine.