North Korea's nuclear weapons program has caused worldwide tension for decades and the rhetoric and threats from Kim and Trump had been especially hostile before their June meeting.
But there was no financial transaction made, which would constitute another violation of the United Nations sanctions, as the companies took coal in return for mediating trade between North Korea and Russia, Roh said.
"I can tell you we continue to have conversations virtually every day, every other day or so with the North Koreans", Heather Nauert, U.S. State Department spokeswoman, said Thursday "When I say 'conversations, ' that can be by phone, that can be my message, that can be by email".
Those American officials are "going against the intention of President Trump to advance the DPRK-U.S. relations, who is expressing gratitude to our goodwill measures for implementing the DPRK-U.S. joint statement", it said referring to the North by its official name, the Democratic People's Republic of Korea.
"Dealing with Americans is hard, and as our main goal is total disarmament of the whole Korean Peninsula, it is necessary that the Americans also abide by their commitments but they refuse to do so".
Satellite images from last Friday indicate North Korea has carried out additional activities to dismantle a key missile launch facility, the Washington-based 38 North think-tank said on Tuesday.
The North Korean government said in a statement through its mission to the United Nations that it has halted nuclear missile tests, dismantled a nuclear test site and begun to return the remains of Americans killed in the Korean War, but lamented continued criticism from USA officials.
"The U.S. should, even at this belated time, respond to our honest efforts in a corresponding manner", North Korea added in its statement.
The newspaper emphasized that North Korea has long made calls for declaring an end to the war and pushed to replace the armistice with a peace treaty, all of which it believes can be realized when the two sides cooperate.
The inter-Korean meeting on Monday will be held at Tongilgak, a North Korean-controlled building in the border village of Panmunjom. It also wasn't clear when another leaders' summit might happen.
Seoul said it accepted the North's proposal after Pyongyang first suggested a meeting Monday to discuss another summit between the leaders.
In the meantime, both Koreas are seeking an end of the Korean War.
Trump's national security adviser, John Bolton, also said this week North Korea has not taken the necessary steps to denuclearise.
Donald Trump has touted the summit with Kim Jong-un in Singapore as a historic breakthrough.