The White House said Thursday it hoped all Afghanistan''s neighbors including Iran would show up to a special conference on the war-torn nation''s future security this month.

Secretary of State Hillary Clinton announced the possible high-level meeting on Afghanistan during her current trip to Europe, and the White House then said it hoped Tehran would be "constructive" if it took part.

"Obviously Afghanistan is something that presents a great challenge, not just for our country, but for the rest of the world," White House spokesman Robert Gibbs said.

"I would expect that Iran would be invited as a neighbor and that we hope, if they decide to come, that they bring constructive solutions and ideas in working with the international community to address the challenges."

Asked whether Clinton or other US officials would meet directly with Iranian envoys to the conference, Gibbs said it was too far down the road to contemplate.

"I am not sure what the exact agenda would be, but obviously we hope that all of Afghanistan''s neighbors are available and that the dialogue is constructive and moves us forward."