US Defense Secretary Robert Gates accused Iran on Friday of playing a "double game" in Afghanistan, by professing to want good ties while undermining NATO-led efforts to provide security.
"Iran is playing a bit of double game in Afghanistan," he told reporters at NATO headquarters in Brussels at the end of two days of talks with his allied counterparts.
"They are an important trading partner for Afghanistan, they profess to have warm relations with the Afghan government," he noted.
"At the same time, they're sending in a relatively modest level of weapons and capabilities to attack ISAF (International Security Assistance Force) and coalition forces.
"They're trying to do what they can to hurt us and hurt our allies and partners in Afghanistan, which also ends up hurting the Afghan people," said Gates.
In March, Iran and NATO held their first talks since the Iranian revolution 30 years ago in signs of a thaw in their ties, when Tehran's diplomat in Brussels met with a senior alliance official.
Iran has close ethnic and religious ties with Afghanistan, but the Islamic republic has suffered badly from the effects of surging opium production, with cheap and readily available heroin fuelling a sharp rise in drug use.