BEIJING — China moved Monday to increase economic pressure on North Korea by implementing a new package of UN sanctions, including a ban on imports of coal, iron, lead, and seafood from its communist neighbor.

The Commerce Ministry said the ban would take effect Tuesday, although China will continue to clear goods that have already arrived in port until Sept. 5.

At the same time, Beijing warned President Trump not to split the international coalition trying to rein in North Korea’s nuclear program by provoking a trade war between China and the United States.

Trump on Monday instructed his top trade negotiator to launch an investigation into Chinese intellectual property violations, a move that could result in trade penalties.

China accounts for about 90 percent of North Korean trade but moved in February to suspend North Korea’s coal imports until the end of the year. Coal usually accounts for about half of North Korea’s exports.

Last month, China announced that total imports from North Korea fell to $880 million in the six months that ended in June, down 13 percent from a year earlier. Notably, China’s coal imports from North Korea dropped precipitously, with only 2.7 million tons being shipped in the first half of 2017, down 75 percent from 2016.

The new import sanctions announced Monday also ban iron and lead ores, as well as seafood products, including fish, crustaceans, and sturgeon caviar. China imported $91 million worth of seafood from North Korea in the first half of 2017, according to Chinese customs figures cited by Reuters.

The latest move to stem imports will put significantly more pressure on North Korea. But analysts say it is unlikely to be enough to persuade Pyongyang to abandon its nuclear program, which it sees as essential to its own survival.

China is very reluctant to do anything that might destabilize the regime, which is a longstanding ally. It blames American hostility toward Pyongyang for forcing the regime to develop its nuclear program, and is urging dialogue to reduce tensions.

In South Korea on Monday, General Joseph Dunford, the chairman of the joint chiefs of staff, told his South Korean counterparts that the United States is ready to use the ‘‘full range’’ of its military capabilities to deal with North Korea.

But Dunford stressed that diplomacy and sanctions were the first plan. ‘‘The military dimension today is directly in support of that diplomatic and economic effort,’’ Dunford told reporters after meeting with South Korea’s president, Moon Jae-in, in Seoul.

‘‘It would be a horrible thing were a war to be conducted here on the peninsula, and that’s why we’re so focused on coming up with a peaceful way ahead,’’ he said, according to Stars and Stripes.

‘‘Nobody’s looking for war,’’ the Marine general said. But he added that the military’s job was to provide ‘‘viable military options in the event that deterrence fails.’’

Dunford was on the first stop of a trip that will also take him to Beijing on Tuesday and then on to Tokyo.

In the meetings with Moon and other officials Monday, Dunford appeared to offer a modified version of the threats that Trump has issued over the past week.

Trump last week warned North Korea that it would face ‘‘fire and fury’’ if it tried to attack the United States or its allies. Then on Friday, after North Korea threatened to launch missiles toward Guam, Trump warned the regime that the American military was ‘‘locked and loaded.’’

Officials in the South Korean government have voiced surprise and confusion at Trump’s tough talk.

Moon, elected as South Korea’s president in May on a pledge to adopt a more conciliatory approach to North Korea, on Monday urged the United States to give diplomacy a chance.

‘‘Peace will not come to the Korean Peninsula by force. Although peace and negotiation are painful and slow, we must pursue this path,’’ he said.

The South Korean leader said conditions for dialogue could be created if North Korea stopped nuclear and missile tests. US military action, he said, requires Seoul’s consent.

Seoul, a metropolitan area of some 25 million people, lies within range of North Korea’s conventional artillery stationed just 30 miles to the North. Hundreds of thousands of Americans, including more than 28,000 US troops, also live in South Korea.

Monday’s meeting came the day before the anniversary of Japan’s defeat in World War II, a day known as ‘‘Liberation Day’’ in both North and South Korea. It also came a week before the US and South Korean militaries are due to start their annual fall exercises, in which they practice responding to an invasion by or the collapse of North Korea. The regime in Pyongyang always strongly objects to the drills, viewing them as a pretext for war.

General Vincent Brooks, commander of US Forces Korea, said the exercises would go ahead as planned.

Meanwhile, The New York Times reported that North Korea’s success in testing an intercontinental missile was made possible by black-market purchases of powerful rocket engines probably from a Ukrainian factory with historical ties to Russia’s missile program. The report cited an expert analysis published Monday and classified assessments by US intelligence agencies.

The studies may solve the mystery of how North Korea began succeeding so suddenly after a string of fiery failures.

Michael Elleman, a missile expert at the International Institute for Strategic Studies, made the analysis.

►China is pressed on intellectual property rights. C2