PYONGYANG, North Korea — Car users in Pyongyang were scrambling Friday to fill up their tanks as gas stations began limiting services or even closing amid concerns of a spreading shortage.

A sign outside one station in the North Korean capital said sales were being restricted to diplomats or vehicles used by international organizations, while others were closed or turning away local residents. Lines at other stations were much longer than usual and prices appeared to be rising significantly.

The cause of the restrictions or how long they might last were not immediately known.

North Korea relies heavily on China for its fuel supply and Beijing has reportedly been tightening its enforcement of international sanctions aimed at getting Pyongyang to abandon its development of nuclear weapons and long-range missiles.

The issue was raised at a regular Chinese Foreign Ministry news conference in Beijing on Friday after a Chinese media outlet, Global Times, reported gas stations were restricting service and charging higher prices.

But spokesman Lu Kang gave an ambiguous response when asked if China was restricting fuel deliveries.

“As for what kind of policy China is taking, I think you should listen to the authoritative remarks or statements of the Chinese government,” he said, without elaborating on what those remarks or statements are. “For the remarks made by certain people or circulated online, it is up to you if you want to take them as references.”

One of China’s top North Korea scholars, Kim Dong-jil, director of the Center for Korean Peninsula Studies of Peking University, said he had not heard of new restrictions on fuel to pressure Pyongyang, but said they are considered to be an option.

China’s Ministry of Commerce had no immediate comment.

Gasoline was selling at $1.25 per kilogram at one station, up from the previous 70-80 cents. According to a sign outside a station where ordinary North Korean vehicles were being turned away, the restrictions took effect on Wednesday.

Gasoline is sold in North Korea by the kilogram, roughly equivalent to a liter (0.26 gallon).

One of China’s top North Korea scholars, Kim Dong-jil, director of the Center for Korean Peninsula Studies of Peking University, said he had not heard of new restrictions on fuel to pressure Pyongyang, but said they are considered to be an option.

China’s Ministry of Commerce had no immediate comment.

When buying gas in North Korea, customers usually first purchase coupons at a cashier’s both for the amount of fuel they want. After filling up the tank, leftover coupons can be used on later visits until their expiration date. A common amount for the coupons is 15 kilograms (19.65 liters or 5.2 U.S. gallons).

Supply is controlled by the state.

The military, state ministries and priority projects have the best access. Several chains of gas stations are operated under different state-run enterprises — for example, Air Koryo, the national flagship airline, operates gas stations as well.

Prices can vary from one station to another.

Traffic in Pyongyang has gotten heavier than in past years, when visitors were often struck by the lack of cars on the capital’s broad avenues.

The greater number of cars, including swelling fleets of taxis, has been an indication of greater economic activity, as many are used for business purposes, such as transporting people or goods.

Associated Press writer Christopher Bodeen in Beijing contributed to this report.