The official, who spoke on the condition of anonymity, said Pyongyang included only one military dog tag with the 55 boxes of remains.
And new satellite imagery from the Sohae Satellite Launching Station on North Korea's west coast suggests workers are dismantling an engine test stand, in line with a promise made to Trump.
Reports had indicated that North Korea was upgrading its only official nuclear enrichment site, and was stepping up enrichment at other secret sites. "Things don't change overnight", Conway later added.
Harry Kazianis, director of defense studies at the Center for the National Interest, a conservative think tank in Washington, said the developments should not be surprising, as North Korea is merely following through on what Kim had said he was going to do during a speech in January.
Secretary of State Mike Pompeo testified last week that verifying North Korea was taking steps toward denuclearizing would "definitely take time", and declined to say publicly whether the regime was making progress on the nuclear front.
"North Korea doesn't recognise exactly where that sea border should be and it's hoped that they can have some agreement to prevent further clashes in the future", he said.
These are not the first reports that North Korea may be continuing its weapons programme, casting doubt on the real impact of the summit in Singapore.
North Korea has provided nearly no information to help identify the individuals whose remains are being repatriated to the United States last week, a US defense official told VOA.
"We see them going to work, just as before", said one USA official, who, like the others, spoke on the condition of anonymity in discussing sensitive intelligence.
Kim Jong Un committed to try to work toward the "complete denuclearization of the Korean Peninsula" during the summit in Singapore, but he agreed to no specific measures or timelines.
United Nations Command Chaplain U.S. Army Col. Sam Lee performs a blessing of sacrifice and remembrance on the 55 boxes of remains thought to be of U.S. soldiers killed in the 1950-53 Korean War, returned by North Korea to the U.S., at the Osan Air Base in South Korea, July 27.
Efforts to recover remains in North Korea have been fraught with political and other obstacles since the war's end.
Lewis's group also published images of a large industrial facility that some US intelligence analysts believe to be the Kangson uranium enrichment plant.
Independent missile experts also told The Washington Post that they have found evidence that is consistent with us agency findings and that there is ongoing activity. Both are in line with Kim's directive during his 2018 New Year's Day address for the country's missile engineers and nuclear scientists to mass produce warheads and missiles.
But the actual details of the process, including how and when the North's nuclear program is to be dismantled, have yet to be worked out.
Foreign-policy experts have remained skeptical about North Korea's intentions, given its history on withdrawing from prior agreements.
This is not the first sign that Trump's summit with Kim was practically meaningless.