North Korean officials on Monday for the first time admitted a months-long surge in gasoline prices in the capital city in the wake of international sanctions.

The prices shot up to one and a half times higher than before starting around April and they remained high, the director of the country's major think tank said in an interview with Kyodo News in Pyongyang.

But Kim Chol, who heads the Economic Institute of the Academy of Social Sciences, said, "The situation is not that the prices are rising continuously or in a state of confusion."

He said that as part of measures to conserve fuel, North Korea has encouraged its people to use public transportation and bicycles.

Kim Jong Guk, an official from the academy, who also attended the interview, said, "(Oil) imports have largely been restricted" as North Korea finds it difficult to transfer money to China or other countries due to financial sanctions, in addition to a decline in the supply.

Reliable data on North Korea are hard to obtain, but the average retail price of gasoline last year is believed have been around $1 per liter.

The official in charge of the academy's external affairs said China has reduced the amount of its oil supply to North Korea, but did not disclose from around when or to what extent.

Despite the spike, there is no visible sign of less car traffic on the streets in Pyongyang and numerous taxis now operating in the country's most developed city have not increased their fares.

North Korea, which carried out an unprecedented test-firing of an intercontinental ballistic missile last week, has been subject to multiple international sanctions. It is banned by the United Nations from testing any nuclear or ballistic missile technology.

The United States has urged China to use its huge economic and political influence in curbing North Korea's nuclear ambitions.

China, meanwhile, has said it has strictly implemented the U.N. sanctions and is against imposing unilateral punitive measures.

It has instead called on the United States and other key players in the region to create a necessary environment for the resumption of negotiations on the North Korean nuclear issue.

U.S. President Donald Trump has been frustrated with China's slowness in meeting his hopes. China accounts for about 90 percent of North Korea's official trade and is a major supplier of oil for Pyongyang.

The Trump administration labeled the Bank of Dandong, based in northeastern China on the border with North Korea, "a foreign bank of primary money laundering concern" late last month and unilaterally sanctioned also another Chinese firm and two Chinese individuals for their connections with Pyongyang's weapons development.

While China has been under more pressure from the United States, the director of the North Korean institute said, "We have a great deal of interest in broadening economic exchanges with Russia."

Kim Chol praised Russia for showing support for North Korea's "independent rights" and opposing the "U.S. hegemony." He suggested that cooperation in such field as energy, construction, light industry, fisheries and transportation can be further promoted between North Korea and Russia, regardless of the international sanctions.

Reflecting North Korea's relatively good relations with Russia, a cargo-passenger ship service linking the two countries started in mid-May.

The North Korean vessel Mangyongbong, capable of carrying about 200 passengers and 1,500 tons of cargo, connects the North Korean port of Rajin and the Russian Far Eastern city of Vladivostok. It is the first passenger ship to travel on a regular basis between the two countries.