South Korean and US forces have stepped up reconnaissance operations amid growing speculation of North Korea's possible test of a long-range missile in the near future, a Seoul military source said Sunday.

A Russian lawmaker who recently visited Pyongyang told media Friday that North Korea is preparing to test a ballistic missile capable of striking the US West Coast.

A Seoul military official said there is no sign that North Korea's provocation is impending.

"But some movements have been continuously detected from the North's missile facilities and bases. We are maintaining the heightened reconnaissance and preparedness posture," the official said. 

US Forces Korea has enhanced the operations of the U-2S ultra-high altitude reconnaissance aircraft and South Korea also increased surveillance with the RC-800 and RF-16 reconnaissance planes, the E-737 airborne early warning and control aircraft and P-3C maritime patrol aircraft, he added.

Maritime and land-based advanced radar systems are running to detect ballistic missiles from North Korea.

Seoul's presidential office has been running a special monitoring system during this year's unusually long 10-day Chuseok fall harvest holiday, which will end on Monday.

Top military officials including Defense Minister Song Young-moo and Joint Chief of Staff Chairman Gen. Jeong Kyeong-doo inspected frontline units and check preparedness during holidays. 

Concerns are growing that North Korea may engage in new provocative acts to coincide with the Oct. 10 founding anniversary of its ruling party, Oct. 9 Columbus Day or the Oct. 18 opening of the 19th national congress by China's Communist Party.

Russia's RIA news agency reported that Anton Morozov, a senior Russian lawmaker, who visited Pyongyang on Oct. 2-6, said the North is preparing for new tests of a long-range missile.

"They even gave us mathematical calculations that they believe prove that their missile can hit the west coast of the United States," RIA quoted Morozov as saying.

"As far as we understand, they intend to launch one more long-range missile in the near future."

North Korea conducted its sixth nuclear test last month and a raft of missile firings in recent months including two intercontinental missile tests in July.

In September North Korean leader Kim Jong-un warned to take the "highest-level" action against the US in response to President Donald Trump's threat to "totally destroy" the regime if necessary. Pyongyang's foreign minister said later it could detonate a hydrogen bomb over the Pacific Ocean. (Yonhap)