Japan's Finance Minister Taro Aso on Thursday pressed his U.S. counterpart Steven Mnuchin to ensure Japanese firms are not hurt by Washington's sanctions on Iran.

The United States' withdrawal from the 2015 Iran nuclear deal means sanctions on financial institutions that do business with Iran will be restored in November.

Aso told a press conference that he relayed to Mnuchin his "hope that Japan's concerns are addressed" in the meeting on the sidelines of a gathering of finance leaders from the Group of 20 major economies.

Firms can avoid the penalties by reducing oil imports from the Middle Eastern country, a condition Tokyo is seeking to utilize.

Aso, who is participating in his first international conference since retaining his Cabinet position in a reshuffle earlier this month, said he and Mnuchin did not discuss trade matters including the recently agreed start of negotiations on a bilateral trade deal.

"We are not the Cabinet members in charge of that," Aso said, referring to Toshimitsu Motegi, Japan's minister in charge of trade talks, and U.S. Trade Representative Robert Lighthizer.

Aso meanwhile said he is paying "close attention" to financial markets following the recent global selloff in stocks that shaved nearly 4 percent off Japan's Nikkei index.