The US request to a UN sanctions committee, a copy of which was obtained by AFP, came as President Donald Trump announced Friday the "heaviest sanctions ever" on North Korea over its nuclear and ballistic missile tests.

Japan joined the United States in supporting the request concerning three of the 33 vessels for carrying out ship-to-ship transfers of oil destined for North Korea in violation of UN resolutions.

Council members have until Friday at 3:00 pm (2000 GMT) to raise objections to the proposed sanctions.

The measures will come into effect if none of the council members, including the North's ally China, block the request.

Only eight vessels have so far been banned from ports for sanctions-busting and the US request would significantly expand the blacklist in a bid to cripple North Korea's maritime network.

Last year, the Security Council adopted a series of resolutions to ban North Korean exports of commodities in a bid to cut off revenue to North Korea's military programs.

The measures severely restrict deliveries of oil and refined petroleum products to North Korea, but a recent report by a UN panel of experts found that Pyongyang was flouting sanctions.

North Korea earned $200 million in revenue last year from exports of coal, iron, steel and other banned commodities, the report said.

The United States and Japan are strong backers of sanctions as a way to pressure Pyongyang to come to the negotiating table and end its drive to develop nuclear weapons.

- Ban on North Korean ships -

Of the 33 vessels that would be hit by the global ban on port entry, a significant number -- 19 -- are from North Korea in a move that could deal a blow to Pyongyang's use of ships to trade in banned goods.

Most of those North Korean tankers, merchant vessels and cargo ships are suspected of taking part in illegal ship-to-ship oil transfers.

The global port ban and UN deflagging would also apply to 13 cargo and tanker ships flagged by various African, South American and Caribbean countries, according to the confidential request sent on Friday.

One ship, the Hao Fan 6, sails under a Chinese flag and is cited for loading North Korean coal at Nampo port in August.

Japan wants three tankers to be banned from ports: the Dominica-flagged Yuk Tung, Belize's Wan Heng 11 and the North Korean tanker Yu Jong 2.

Japanese military patrol planes spotted the transfer of oil cargo involving the Yu Jong 2 in the East Sea earlier this month and reported it to the UN sanctions committee.

The US request targets a national from Taiwan, Tsang Yung Yuan, who is said to be coordinating illegal North Korean coal exports with a North Korean broker in Russia.

Of the 27 shipping and trading firms facing a UN assets freeze, five are based in Hong Kong including Huaxin Shipping, which has allegedly used its vessel to deliver North Korean coal to Vietnam.

Two other companies -- Shanghai Dongfeng Shipping and Weihai World Shipping Freight -- also based in China, are cited for carrying North Korean coal on their vessels.