Japanese Prime Minister Shinzo Abe on Thursday said that North Korea could be capable of firing a missile carrying sarin gas at Japan, according to reports.

“There is a possibility that North Korea is already capable of delivering a warhead containing sarin,” Abe told a parliamentary committee on national security.

The warning comes amid heightening tensions between the U.S. and North Korea. The U.S. deployed a Navy strike group to the west Pacific near the Korean Peninsula over the weekend as concerns grow over the country's weapons program.

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North Korea responded by denouncing the move as an aggression and threatening a nuclear strike if the U.S. were to take military action.

Japan is one of the U.S.'s closest allies in the region and is considered a prime target for a North Korean missile strike because of its proximity to the Korean Peninsula. While the north's continued development of nuclear warheads has been a top issue of concern, Abe stressed that the country already had the ability to fire a sarin-tipped missile at Japan.

Sarin is a nerve agent banned by the United Nations chemical weapons convention and is capable of killing victims within minutes.

The Trump administration has said that the U.S. is keeping a military option in the region on the table, but is leaning toward a diplomatic and economic solution to the rising tensions with North Korea.