SEOUL: North Korea appeared to have conducted artillery firing drills on Sunday, its southern neighbor said, days after the United States deployed sophisticated fighter jets to South Korea for joint training.

In a statement, South Korea's Joint Chiefs of Staff said it detected multiple trajectories presumed to be North Korean artillery on Sunday afternoon. Seoul's military maintained firm readiness in close coordination with the US, it added.

South Korea's presidential office said the suspected launches occurred off the North's western coast. Presidential national security director Kim Sung-han has reviewed South Korean military readiness and his office closely monitors possible additional launches by Pyongyang, it added.

North Korea has carried out an unusually large number of weapons tests this year, including nuclear-capable missiles that place both the US mainland and its allies, including South Korea and Japan, within striking distance. Some experts say the North's attempts to perfect its weapons technology and boost its bargaining chip in future negotiations with Washington to win sanctions relief or security guarantees.

Last week, six US F-35 aircraft from the Eielson Air Force Base in the US state of Alaska arrived in South Korea for their first temporary deployment there in about four-and-a-half years for joint training with Seoul's fighter jets.

South Korea's Defense Ministry said the jets' deployment was aimed at demonstrating the allies' combined defense posture and strong deterrence against potential external aggression while improving the interoperability of the two air forces. A US military statement said the American aircraft planned to operate over the South and its surrounding waters during the scheduled 10-day training mission.

North Korea typically views joint exercises between the US and South Korea as an invasion rehearsal and responds with its own weapons tests. Washington and Seoul defense officials have repeatedly said they have no intentions of attacking the North.

Pyongyang has said it was forced to develop nuclear weapons to cope with US military threats. Despite its torrid run of missile tests earlier this year, the country hasn't conducted its expected first nuclear bomb test in five years, and Seoul officials said that was likely because of an ongoing Covid-19 outbreak and opposition by China, its last major ally and aid benefactor.