The man was gunned down in Kabul hours after the Taliban claimed to have published a top-secret security plan for the loya jirga, which starts Wednesday and will bring together over 2,000 elders from around the country.

Afghan officials and the NATO-led foreign military in Afghanistan said the document was fake, but the leak and the killing highlight tight security around the jirga as the Taliban threatens to target those taking part.

Security forces shot the would-be bomber as he carried explosives, interior ministry spokesman Sediq Sediqqi said.

"No one was killed but the bomber," he added.

Lutfullah Mashal, spokesman for Afghanistan's intelligence service the National Directorate of Security, said the man's bag blew up as he was shot.

"A suicide bomber who wanted to enter the polytechnic university (where the loya jirga will take place) was identified and shot dead by security forces.

"His explosives detonated as he was shot dead... He was carrying the explosives in a laptop-type bag," Mashal said.

The loya jirga will discuss the US-Afghanistan strategic partnership, which is still under negotiation but will govern the two countries' relations after 2014, when all foreign combat troops are due to leave.

It will also cover the Afghan government's efforts to make peace with the Taliban, which were dealt a heavy blow by the assassination in September of President Hamid Karzai's peace envoy Burhanuddin Rabbani.