US President George W Bush [Images] said during his first visit to Afghanistan Wednesday that Iran must not be allowed to develop nuclear weapons.

• Bush's India Visit

"Iran must not have a nuclear weapon," Bush said during a joint press conference with Afghan President Hamid Karzai [Images] in Kabul.

"The most destabilising thing that can happen in this region and in the world is for Iran to develop a nuclear weapon, so the world is speaking with one voice," the US leader added.