TOKYO, March 5 (Xinhua) -- Tokyo stocks closed lower Monday, with the benchmark Nikkei stock index falling to its lowest level in almost five months as the yen's rise hurt exporters and concerns about U.S. protectionism continued.

The 225-issue Nikkei Stock Average lost 139.55 points, or 0.66 percent, from Friday to close the day at 21,042.09.

The broader Topix index of all First Section issues on the Tokyo Stock Exchange, meanwhile, fell 13.55 points, or 0.79 percent, to finish at 1,694.79.

Local brokers here said that investors were becoming increasingly cautious about a potential new U.S. trade policy that could be announced soon, following U.S. President Donald Trump's remarks about tariffs on steel and aluminum imports.

They said that the move could result in other countries also imposing new tariffs on imports which could lead to a trade war.

The yen's rise against the U.S. dollar further sullied the market mood and saw exporters dragged lower, market players said.

Companies with a wide exposure to overseas markets rely on a weaker yen to boost their profits and competitiveness overseas and see yields augmented when repatriated on favorable exchange rates.

A firm yen also clouds the outlook for export-related firms' corporate earnings, which are usually pegged to a weaker yen.

Market strategists said that in late trade bargain hunting helped pare some of the losses, but fears of the United States' protectionist stance would likely linger on and hurt sentiment in the coming days.

Nonferrous metal, marine transportation, and iron and steel-linked issues comprised those that declined the most by the close of play, and falling issues beat advancing ones by 1,532 to 482, on the First Section, with 55 ending the day unchanged.

On the main section on Monday, 1,510.45 million shares changed hands, dropping from Friday's volume of 1,601.00 million shares.

The turnover on the first trading day of the week came to 2,761.7 billion yen (26.20 billion U.S. dollars).