A would-be suicide bomber fell down a flight of stairs and blew himself up as he headed out for an attack in Afghanistan, police say.

It was the second such incident in two days, with another man killing himself and three others on Tuesday when his bomb-filled waistcoat exploded as he was putting it on in the southern town of Lashkar Gah.

Yesterday's blast was in a busy market area of the eastern town of Khost, a deputy provincial police chief said.

The would-be attacker tripped as he was leaving a building apparently to target an opening ceremony for a mosque that was expected to be attended by Afghan and international military officials, said Sakhi Mir.

"Coming down the stairs, he fell down and exploded. Two civilian women and a man were wounded,'' Mir said.

Suicide attacks are regular feature of an insurgency led by the extremist Taliban movement that was in government between 1996 and 2001. The most deadly was in November 2007 and killed nearly 80 people, most of them school students.