Miliband said that the invitation had been extended to his Iranian counterpart Manouchehr Mottaki to the conference called by British Prime Minister Gordon Brown on January 28, the Islamic republic news agency reported.
The meeting is seen "as a chance to, for the whole region but also the wider international community to support decent Government in Afghanistan and that's what we need to do," Miliband said in an interview with the BBC.
Brown said on Monday that 68 international delegations will come to London for the conference.
"All 43 powers engaged in the international coalition will attend, together with other regional and Muslim partners and international organizations," he said.
He said the gathering will be led by the Secretaries-General of the United Nations and NATO but also added that it was also "right" for regional neighbors to attend.
"It is very important to recognize that in the longer term Afghanistan's future is dependent on both non-interference by its immediate neighbors and economic and cultural co-operation between Afghanistan and its neighbors," the British premier said.
During last weekend's visit to Afghanistan, he said he had agreed with President Hamid Karzai that the aim of the conference was to deliver a "new compact between Afghanistan and the international community on priorities that he has outlined."
"The first of those priorities is security. We expect nations to announce troop deployments building on the total of 140,000 troops promised for 2010," Brown told MPs.
"I hope the London conference will also be able to set out the next stage in a longer-term plan: the changing balance between alliance forces and Afghan army and defense forces as the number of Afghan forces increases from 90,000 to 135,000 next year and possibly to 175,000 later."
The second priority was for NATO and its allies to set out an outline program for the transfer of lead responsibility to Afghan forces, which Brown hoped could begin during 2010.
The other main aims related to gaining international support and financial backing for Afghan-led resettlement, reintegration and economic development as well as addressing the issue of co-coordinating international efforts on Afghanistan.
"London must also encourage a new set of relationships between Afghanistan and its neighbors, and, in particular, better joint working with Pakistan," Brown further said.