UNITED NATIONS -- The U.N. Security Council has banned all nations from allowing four ships that transported prohibited goods to and from North Korea to enter any port in their country.

Hugh Griffiths, head of the panel of experts investigating the implementation of U.N. sanctions against North Korea, announced the port bans at a briefing to U.N. member states on Monday. A North Korean diplomat attended the hour-long session.

Griffiths later told several reporters that "this is the first time in U.N. history" that the Security Council committee monitoring sanctions against Pyongyang has prohibited ships from entering all ports.

The ban on the ships is significant as it generally takes much more time for Security Council sanctions resolutions to take effect, explains CBS News' Pamela Falk. The four vessels were identified and banned in record time -- with crucial support from China to enforce the move.

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Last month, the panel of experts had found dozens of member states evading sanctions, so the ship ban is a step in the right direction, and more enforcement is in the works, Falk reports, as the U.N. works to make it more costly for North Korea to conduct prohibited trade.

Griffiths identified the four cargo ships as the Petrel 8, Hao Fan 6, Tong San 2 and Jie Shun.

According to MarineTraffic, a maritime database that monitors vessels and their moments, Petrel 8 is registered in Comoros, Hao Fan 6 in St. Kitts and Nevis, and Tong San 2 in North Korea. It does not list the flag of Tong San 2 but said that on Oct. 3 it was in the Bohai Sea off north China.

Griffiths said the four ships were officially listed on Oct. 5 "for transporting prohibited goods," stressing that this was "swift action" by the sanctions committee following the Aug. 6 Security Council resolution that authorized port bans.

That resolution, which followed North Korea's first successful tests of intercontinental ballistic missiles capable of reaching the United States, also banned the country from exporting coal, iron, lead and seafood products. Those goods are estimated to be worth over $1 billion - about one-third of the country's estimated $3 billion in exports in 2016.

The Security Council unanimously approved more sanctions on Sept. 11, responding to North Korea's sixth and strongest nuclear test explosion on Sept. 3.

These latest sanctions ban North Korea from importing all natural gas liquids and condensates, and cap its crude oil imports. They also prohibit all textile exports, ban all joint ventures and cooperative operations, and bars any country from authorizing new work permits for North Korean workers - key sources of hard currency for the northeast Asian nation.

Both resolutions are aimed at increasing economic pressure on the Democratic People's Republic of Korea - the country's official name - to return to negotiations on its nuclear and missile programs.

The ship ban was announced as U.S. Defense Secretary James Mattis reiterated the White House's official commitment to the U.N.-led diplomatic effort to rein-in North Korea, but warned that the world's most powerful military "must stand ready" in the face of Kim Jong Un's continued provocations.

While delivering the keynote address at the Association of the U.S. Army's annual meeting on Monday, Mattis outlined the current strategy in North Korea for the Trump administration, saying "it is right now diplomatically led, economic sanctioned, buttressed effort to try to turn North Korea off its path."

He conceded, however, that "neither you nor I can say" what the future holds for the regime.

Griffiths told U.N. diplomats that the panel of experts is getting reports that the DPRK "is continuing its attempts to export coal" in violation of U.N. sanctions.

"We have as yet no evidence whatsoever of state complicity, but given the large quantities of money involved and the excess capacity of coal in the DPRK it probably comes as no surprise to you all that they're seeking to make some money here," he said.

Griffiths said the panel is "doing our very best to monitor the situation and to follow up with member states who maybe have been taken advantage of by the tactics deployed by DPRK coal export entities."

As for joint ventures and cooperative arrangements, Griffiths said the resolution gives them 120 days from Sept. 11 to close down.

But "in a number of cases, the indications are that these joint ventures aren't shutting down at all but are on the contrary expanding - and therefore joint ventures is a major feature of the panel's current investigations," he said.

Griffiths also asked all countries to pay "special attention" to North Korea's Mansudae Overseas Project Group of Companies, also known as the Mansudae Art Studio, which is on the sanctions blacklist and subject to an asset freeze and travel ban.

According to the sanctions listing, Mansudae exports North Korean workers to other countries "for construction-related activities including for statues and monuments to generate revenue for the government of the DPRK or the (ruling) Workers' Party of Korea."

Griffiths said Mansudae "has representatives, branches and affiliates in the Asia-Pacific region, all over Africa and all over Europe. Without elaborating, he added that "they're doing an awful lot more than producing statues in Africa."