"Substantive and detailed meetings in #Singapore today as Ambassador Kim meets with #DPRK," Pompeo wrote in a Twitter post in which he included a photograph of the meeting between US Ambassador to the Philippines Sung Kim, North Korean Foreign Ministry senior official Choi Sun Hee and other delegates from both countries.
Later in the day, Pompeo said, that the talks are moving "quite rapidly" and confirmed, that the US is ready to provide "unique" security assurances for North Korea to engage its denuclearization, adding, however, that the pressure on Pyongyang would rise significantly if the diplomatic approach fails.
US State Secretary also claimed that President Trump may consider lifting some economic restrictions if the North Korean government takes the "right steps."
"The president has also expressed his openness to expanding access to foreign investment and other economic opportunities for North Korea if they take the right steps," Pompeo told reporters.
The two sides met to narrow differences ahead of Tuesday's summit between Trump and Kim, at which the two leaders will discuss efforts to denuclearize the Korean peninsula.
Earlier in June, media reported that Pyongyang, during summit preparations, had demanded that the United States lift the sanctions against North Korea and establish diplomatic relations with the country.