Afghan Foreign Minister Zalmai Rasoul arrived in Tehran on Sunday on the first high-level visit by an Afghan official since President Hamid Karzai admitted Kabul had received Iranian cash payments.
Rasoul's visit also comes as Iran is still holding seven Afghan military personnel who strayed across the border last month. Iran's ISNA news agency reported that Rasoul headed a delegation including several deputy ministers that sought to boost relations between Kabul and Tehran.
Karzai's administration was plunged into controversy last month after the New York Times reported that his chief of staff, Umar Daudzai, had received regular cash payments from Iran.
The report cited officials as saying the payments were intended to secure the allegiance of Daudzai, a former ambassador to Tehran who briefs Karzai daily and consistently advocates an anti-Western line.
The Iranian foreign ministry later acknowledged giving "assistance" to Afghanistan. Karzai denied that the payments were secret and likened them to the financial assistance given to Kabul by Washington.
Iran, meanwhile, is still holding seven Afghan military personnel who "inadvertently" crossed into the Islamic republic last month while chasing Taliban militants.
Iran's Mehr news agency quoted the commander of the border police, Hossein Zolfaqari, as saying that Tehran would release them soon.
The seven, including six officers and a soldier, reportedly said that they were hunting for Taliban militants when they strayed into the Iranian border province of Sistan-Baluchestan where they were arrested.
Sistan-Baluchestan borders both Afghanistan and Pakistan, and is an area rife with ethnic unrest and drug smuggling