A high-ranking North Korean figure appears to be currently visiting China, sources close to the matter said Monday, but it has yet to be confirmed whether that is the country's leader Kim Jong Un.

The extra tight security has prompted speculation that an important foreign dignitary is now in the Chinese capital, the sources said.

If the dignitary is really from North Korea, the purpose of the trip would likely be to improve bilateral relations that have been strained over Pyongyang's nuclear ambitions, they said.

As Beijing has tightened economic sanctions against Pyongyang, the North Korean visitor could also seek their relaxation and the provision of economic cooperation such as food aid and investment.

Kim has reportedly agreed to hold summits with South Korean President Moon Jae In and U.S. President Donald Trump, separately.

On Sunday, a special train that might have carried the North Korean visitor passed through the Chinese border city of Dandong, the sources said.

If Kim is really visiting China, it would be his first trip to another country since becoming North Korea's supreme leader after the death of his father Kim Jong Il in 2011.

(Photo taken in August 2010 in China shows a special train used by the then North Korean leader Kim Jong Il)

In Beijing, a car with a diplomatic license plate of the North Korean Embassy was spotted Monday at the Great Hall of the People, a state building used for activities by the government and the ruling Communist Party of China.

Severe traffic regulations were enforced in Beijing on Monday.

Hotels around the Sino-Korean Friendship Bridge linking Dandong with the North Korean town of Sinuiju have suspended reservations for rooms facing the North Korean side since Sunday, in an apparent move to prevent the train from being seen.

But some diplomatic sources in Beijing are skeptical whether Kim is staying in China, as accompanying cars do not bear North Korea's national flag as would normally be the case in the case of a visiting foreign leader.

The visitor might be North Korea's ceremonial leader Kim Yong Nam or Choe Ryong Hae, the nation's de facto No. 2 figure who is regarded as Kim's right-hand man, the sources added.

Kim and Chinese President Xi Jinping have never met.

Kim's father, who was known for shunning air travel, visited China four times by train between 2010 and 2011.