It was the second round of bilateral negotiations on Washington's decision to resume a wide web of sanctions against Tehran. The previous talks were held in Seoul in June.

The US has pressed Korea and some other nations to halt their oil imports from the OPEC member or face so-called secondary sanctions with the May announcement of its exit from the 2015 nuclear agreement with Iran, called the Joint Comprehensive Plan of Action. The 180-day grace period is to end on Nov. 4.

Seoul hopes for a conditional waiver, similar to a measure put in place under the Obama administration. At that time, Korea significantly reduced its oil imports from Iran.

The Northeast Asian country is not an oil producer and more than 13 percent of its total oil purchases come from Iran.

What's especially crucial is condensate -- ultra light oil -- used for the production of various petrochemical goods. Iran's condensate is known for its high quality.

It's also important to maintain Iranian oil imports for the won-based settlement of bilateral trade transactions.

Korean refiners put money into bank accounts here for oil imports from Iran, whose firms pay for the purchase of Korean products through them.

The two-way trade volume totaled $12 billion in 2017, with Korea exporting $4 billion worth of products.

In the bargaining, Yun explained the government's basic stance of support for a peaceful resolution to the Iranian nuclear issue, said the Ministry of Foreign Affairs.

He also emphasized that Korea should be granted a waiver to minimize the impact to its companies doing businesses with Iran, citing the special conditions facing them.

"He proposed that the governments of the two nations cooperate more closely on the basis of the alliance spirit," the ministry said.

Although the US reiterated that it will be quite stringent in granting a waiver this time, it promised to consider Korea's positions, added the ministry.

The two sides apparently plan to continue talks but no schedule has been set.