Tokyo's benchmark index on Friday fell to its lowest close this year as geopolitical fears spiked after the US dropped a massive bomb in Afghanistan.
The Japanese market led Asian bourses lower with investors jittery after the Pentagon announced it dropped the largest non-nuclear bomb ever deployed in combat, targeting an Islamic State complex.
US President Donald Trump called the mission "very, very successful," but the announcement added to concerns for markets already wary of risks over Syria and North Korea, as well as the outcome of the French presidential election.
"It's just creating more uncertainty with people," Frank Ingarra, head trader at US-based NorthCoast Asset Management, told Bloomberg News.
The Nikkei 225 dropped 0.49 percent, or 91.21 points, to end the session at 18,335.63, marking a weekly loss of 1.76 percent.
The broader Topix index of all first-section issues meanwhile fell 0.63 percent, or 9.24 points, to 1,459.07. It was down 2.06 percent over the week.
In other Asian markets, the benchmark Shanghai Composite Index dipped 0.91 percent, or 29.89 points, to 3,246.07.
The Shenzhen Composite Index, which tracks stocks on China's second exchange, fell 1.39 percent, or 28.02 points, to 1,986.65.
South Korea's Kospi ended the day 0.64 percent, or 13.73 points, lower at 2,134.88.
Markets in Hong Kong, Singapore, Sydney and Mumbai were closed for a holiday.
The latest US assault came only a week after Trump ordered missile strikes against Syria in retaliation for a suspected chemical attack.
Trump has also said he is keeping "all options" on the table to stop North Korea's nuclear programme, as speculation mounts that Pyongyang may soon hold another nuclear test.
"Towards the end of trading, reports came that North Korea was further hardening its position," Okasan Online Securities said in a commentary.
"The reports accelerated (the market's) fall."
Geopolitical worries are expected to continue affecting global markets in the coming week, when investors will also see a range of key data released, including Chinese factory production and retail sales as well as January-March GDP figures.
The US Federal Reserve's "beige book" survey of the US economy could also set the market's direction.
In Tokyo trading, Nintendo jumped 2.06 percent to 25,760 yen, after the videogame giant said it sold over 900,000 units of its new Switch console in North America last month.
Uniqlo operator Fast Retailing rose 1.36 percent to 35,330 after reporting strong earnings Thursday.
Toshiba fell 5.42 percent to 198.7 yen, as Bloomberg News reported the company was temporarily cancelling all meetings tied to the sale of its memory chip business.
Toshiba denied the report, and the stock pared losses in early afternoon trading as Japan's public broadcaster NHK said Apple was considering investing in the chip division.
In currency markets, the dollar bought 108.91 yen, slipping from 109.14 yen in New York, while the euro was little changed at $1.0616, against $1.0613.