Singapore says it refused an Australian man entry to the city-state due to his history of extremism and sent him home.

Zaky Mallah was denied entry on Wednesday as Singapore prepares to host a historic meeting next week of President Donald Trump and North Korean leader Kim Jong Un.

Singapore's Ministry of Home Affairs said in a statement the 34-year-old was denied entry "on account of his terrorism-related antecedents."

The ministry referred to Mallah in 2003 becoming the first person charged under new Australian counterterrorism laws with planning a suicide attack.

The statement says he was acquitted of charges of preparing a terrorist act in 2005, but received a 2 ½ -year jail sentence after pleading guilty to threatening violence against Australian government officials.