Iran has for the first time taken part in high-level discussions on Afghanistan after the US said it had "no problem" with its participation.
An Iranian representative joined the international "contact group" - which brings together the Afghan government, dozens of countries, Nato, the EU and UN - for the talks in Rome.
It comes amid a renewed push to end the bloody nine-year Afghan conflict.
One senior US diplomat said Iran had "a role to play" in tackling the problems.
"We recognise that Iran, with its long, almost completely open border with Afghanistan and with a huge drug problem... has a role to play in the peaceful settlement of this situation in Afghanistan," Richard Holbrooke - the US special representative to Afghanistan and Pakistan - told a news conference.
"So for the United States there is no problem with their presence."
He said discussions would not be affected by the "bilateral issues" of Iran's nuclear programme, which Iran says is for purely civilian purposes but the US insists is a cover for creating atomic weapons.
Iran sent its special envoy for Afghanistan and Pakistan, Mohammed Ali Ghanazadeh, reported Associated Press.
BBC News
