Hugh Griffiths, the coordinator for the UN Panel of Experts on North Korea, called the move "swift and decisive."
The port bans were enacted under UN Security Council Resolution 2375, which was passed last month after North Korea test-fired a missile that overflew Japan.
It is the first time the United Nations Security Council 1718 Committee, which oversees sanctions imposed by the Security Council on North Korea, has designated ships for port bans, according to Griffiths.
The UN said the four ships were the Jie Shun, the ship caught smuggling grenades
; the Hao Fan 6, the Petrel 8 and and the Tong San 2.
The Hao Fan 6 is registered in St. Kitts and Nevis, tiny islands in the Caribbean, while the Petrel 8 is a cargo ship registered in the Comoros islands, off the coast of East Africa; according to MarineTraffic.com.
The Jie Shun is registered in Cambodia, while the Tong San 2 is under the North Korean flag.
North Korea has for years has been accused of evading international sanctions to fund everything
from its nuclear program to the lavish lifestyles of Pyongyang's biggest players.
US President Donald Trump's administration is now going after North Korea's money as part of its campaign to rein in the hermit nation's weapons programs.
Its plan is to further isolate the regime of North Korean leader Kim Jong Un diplomatically and cut off its access to the international financial system in the hopes that it will eventually put its nuclear weapons and ballistic missiles on the negotiating table in exchange for sanctions relief.
However, North Korea maintains that its nuclear program is for deterrence purposes to protect itself against the threat of a US-led invasion. Some analysts believe that North Korea sees the nuclear program as key to the country's survival, making it unlikely that they will give it up.