WASHINGTON (Reuters) - The U.S. Treasury Department tightened sanctions against North Korean diplomats to the United Nations, requiring banks to get special permission before granting them accounts, the agency said in a notice posted online Tuesday.

The United States removed an exemption in the broad economic sanctions against Pyongyang that had allowed U.S. banks to service North Korean diplomats without getting specific permission from the Treasury Department Office of Foreign Assets Control (OFAC).

Banks will now have to obtain a special license from OFAC before opening bank accounts, processing transactions or extending credit for North Korean diplomats or their family members, OFAC said. North Korea’s U.N. mission did not immediately respond to a request for comment.

U.S. officials have long said North Korea uses the bank accounts of diplomats to help Pyongyang conduct business around the world, despite economic sanctions.

A U.S. intelligence official, speaking on condition of anonymity, said North Korea “seeks to alleviate its economic isolation” by bringing back currency from overseas “using all available avenues.”

For example, said another U.S. intelligence official, North Korea sells cigarettes and illegal drugs outside the country and use diplomatic packages to send the cash back home.

Washington has been ramping up economic sanctions against Pyongyang since a nuclear test and rocket launch this year, seen as provocations by the United States and its allies.

Under new U.N. sanctions adopted last month in response to North Korea’s fifth and largest nuclear test in September, countries are required to limit the number of bank accounts to one per North Korean diplomatic mission and one per diplomat.