North Korea is touting a "great leap forward" in its rocket industry after the successful testing of a new high-thrust engine, state media reported Sunday.

Malaysia's police chief said Sunday that authorities are looking for more North Korean suspects including an "important person" suspected of involvement in last month's assassination of Kim Jong Nam, the estranged half-brother of North Korean leader Kim Jong Un.

The test measured the thrust power in the combustion chamber, the structural safety and reliability of the engine, and the movement of the turbine pump, state-owned Korean Central News Agency reported.

"The leader (Kim) noted that the success made in the current test marked a great event of historic significance as it declared a new birth of the Juche-based rocket industry". "The photos released by North Korea suggest that it's attempting to make the first stage of an ICBM by attaching supplemental engines that serve as the rocket steering mechanism to a more efficient main engine instead of the [clustering] approach, in which several engines are tied together", said Kim Dong-yeop, a professor at the Kyungnam University Institute for Far Eastern Studies.

U.S. President Donald Trump told reporters he held meetings on North Korea at the weekend at his Florida resort.

The alleged test was announced on the same day that U.S. Secretary of State Rex Tillerson visited China - which has backed North Korea in a somewhat complex relationship - and a day after Tillerson said that all options to meet North Korea's weapons programs remained "on the table".

"He's acting very very badly", the president said of Kim Jong Un, according to a White House pool report.

Kathleen Stephens, a former US Ambassador to South Korea, said that all these indicates that the US is toughening its stance against North Korea. North Korea will do this to defend the security of their country as well as its people's happiness.

Mr Tillerson said the USA did not want a military conflict, but if North Korea took actions that threatened South Korean forces or United States forces, "that would be met with [an] appropriate response".

Earlier in February North Korea test-fired a ballistic missile, which is believed to have splashed down into the sea between the Korean Peninsula and Japan.

South Korea's trade minister confirmed Monday that Seoul has officially appealed to the World Trade Organization against China's moves, which have affected trade, tourism and culture.

The United Nations forbids North Korea from conducting long-range missile tests, but allows its satellite program for peaceful use.

North Korean officials have said that under a five-year plan they intend to launch more Earth observation satellites and what would be the country's first geostationary communications satellite - which would be a major technological advance.

Relations have also been strained by China's fierce opposition to a U.S. missile defence system being rolled out in South Korea and Mr Trump's Twitter accusation on Friday that China was not doing enough to control Pyongyang, its neighbour and historic ally. There is no need to fixate on every word he says, but past USA secretaries of state have not referred to South Korea that way.