North Korea is mobilizing all of its people ahead of a key party congress in May by pressing them to work hard even at night and on weekends, sources said Wednesday.

The North has been pushing its people, including those in Pyongyang, to put in long hours in a bid to achieve short-term goals before the ruling Workers' Party of Korea holds its congress early next month, according to sources familiar with the isolationist country.

"North Koreans are working every day from 7:00 a.m. to 9:00 p.m. as the regime is intensifying its '70-day campaign of loyalty' for the congress," a source said. "Their complaints are growing."

Seoul's spy agency forecast the event will be held on May 7.

The sources said that North Koreans living in Pyongyang are no exception, a clear sign that the North's leadership will not accept complaints even from those living in the capital, who are viewed as being relatively privileged.

North Korea is also pushing its government organs to collect money for the party event as the U.N. sanctions are making it harder for the regime to secure hard currency, the sources said.

The North has forcefully set the amount of money that has to be collected for the party as the U.N. sanctions ban exports of mineral resources, a main source of dollars for the cash-strapped North.

Last month, the United Nations Security Council imposed the toughest sanctions in decades on North Korea for its January nuclear test and long-range rocket launch in February.

China, the main ally for the North, said Tuesday that it will restrict imports of North Korean coal and iron ore, and ban exports of jet fuel to the North, in accordance with new U.N. sanctions.

North Korea is known to have ordered its government agencies to raise funds for the construction of a new developed district in Pyongyang, named "Ryomyong Street," the sources added.

They said that North Korea remains jittery as its exports of zinc to China hit a snag due to Beijing's announcement.

"The North's exports of zinc to China had been the main source of hard currency. But North Korea is concerned as its main export channel is blocked," the source said.

Seoul's unification ministry welcomed China's voluntary move to restrict imports of North Korean mineral sources.

"The government believes that China's actions will significantly contribute to helping the U.N. sanctions gain consensus globally and be fully enforced," Jeong Joon-hee, a ministry spokesman, said at a regular press briefing. (Yonhap)