One day after the Asian security summit in the Philippines, Tillerson visited Thailand and Malaysia.
Susan Thornton, acting assistant secretary of the State Department's East Asian bureau, said Tillerson asked Thailand's ruling military junta to take the lead against North Korea in an attempt to curb the regime's intercontinental missile testing.
Tillerson was the highest-ranking U.S. official to visit Thailand since a coup there in 2014. He met with Prime Minister Prayuth Chan-ocha and Foreign Minister Don Pramudwinai in Bangkok.
"The secretary discussed the broad range of U.S.-Thai cooperation on regional security, trade and investment, and other areas, including through regional forums like ASEAN," a U.S. Embassy spokesperson said in a statement to Voice of America. "He also raised regional and global issues, including the security threat posed by DPRK [North Korea], as well as developments in the South China Sea."
Tillerson then spoke with Malaysian Prime Minister Najib Razak in Kuala Lumpur.
Many Asian countries maintain diplomatic and economic relationships with North Korea, which officials believe allows the regime to evade sanctions. North Korea maintains eight embassies in Southeast Asia, including in Thailand, Malaysia and Indonesia.
On Saturday, the United Nations Security Council unanimously passed new sanctions against North Korea. One week earlier, North Korea launched the second of two missiles that officials said would be capable of striking the U.S. mainland.
"Southeast Asia is a logical place to focus on," Sheena Greitens, an assistant professor of political science at the University of Missouri told The Wall Street Journal. "Many of the existing U.N. sanctions on the books already aren't strictly enforced, and so the effect of recent measures such as the U.N. resolution is going to depend heavily on how seriously countries take enforcement."
China is North Korea's largest trading partner, but Thailand and the Philippines were among its top five largest import partners in 2015, according to estimates by trade experts. Malaysia and Singapore also are among a few nations in the world to offer visa-free travel to North Korea.
Philippine foreign secretary Alan Peter Cayetano said Tuesday that the Southeast Asia nations are open to negotiating with North Korea but the regime is unwilling.
"We're saying how can you play peacemaker if they will not open a door or they will not listen?'' Cayetano said. "They are not giving us a choice."