HONG KONG — Under growing pressure from the United States, some of Asia’s largest economies are reluctantly looking for options to reduce the amount of oil they buy from Iran, a move that would further tighten the economic vise on an increasingly defiant nation that announced plans for a new round of naval drills in the Strait of Hormuz.

The decision by South Korea and Japan to try to accommodate Washington’s demands follows reports that China has already reduced its purchase of Iranian crude in the past month in a pricing dispute with Tehran. Whatever the motives, the combined loss of sales threatens an economy already reeling, where the currency has plummeted in value, inflation has surged and the general public has expressed growing anxiety about the prospect of war.

China, Japan, India and South Korea together import more than 60 percent of Iranian oil exports, and they all depend on Iran and other Persian Gulf producers for the preponderance of their oil and natural gas needs. As tensions in the gulf have escalated and alarmed Asian governments and businesses, companies and traders from those countries have been putting out feelers to places like Russia, Vietnam, West Africa, Iraq and especially Saudi Arabia to export more oil to them, according to oil experts.

For Tehran, which relies heavily on oil revenues to prop up an economy battered by years of sanctions, the potential cutbacks by its Asian customers follow a decision by the European Union to move toward a ban on the import of Iranian oil. Taken together, the Western efforts represent the most serious economic pressure yet on Iran after years of conflict over a nuclear program that the West charges is aimed at building weapons.