Tokyo stocks closed lower Monday, with the Nikkei benchmark index falling to a three-and-a-half month low over concerns geopolitical tensions may rise further on the Korean Peninsular following the start of annual U.S.-South Korean military exercises.

The 225-issue Nikkei Stock Average dropped 77.28 points, or 0.40 percent, from Friday to finish the day at 19,393.13, marking its lowest close since early May.

The broader Topix index of all First Section issues on the Tokyo Stock Exchange, meanwhile, closed 2.17 points, or 0.14 percent, lower at 1,595.19.

Securities, bank and rubber product-linked issues comprised those that declined the most by the final bell, and rising issues outpaced falling ones by 1,038 to 852 on the First Section.

Traders here said, geopolitical concerns aside, stocks also retreated over concerns for the future course of the administration of U.S. President Donald Trump, amid upheavals in the White House and policy issues.

Pressure on selling eased in later trade, however, brokers said, as investors sought out bargains following the market's slump late last week.

On the main section on Monday, 1,406.90 million shares changed hands, dropping from Friday's volume of 1,671.73 million shares.

The turnover on the first trading day of the week came to 1,753.4 billion yen (16.07 billion U.S. dollars).