U.S. Secretary of State Mike Pompeo on Friday pushed Turkey to release a detained American pastor whose case prompted the Trump administration to slap sanctions on senior Turkish officials, and said North Korea is still lagging behind on its promise to denuclearize.

Pompeo made the remarks before attending separate meetings with top Turkish and North Korean officials on the sidelines of a Southeast Asian security conference in Singapore.

He urged the Turkish government to release Andrew Craig Brunson, the American pastor detained in Turkey since December 2016 on espionage and terror-related charges, which both Brunson and the U.S. vehemently deny.

The administration is also seeking the release of several detained local employees of the U.S. diplomatic missions in the Turkey.

Pompeo said the administration’s actions on Wednesday – imposing sanctions on Turkey's justice and interior ministers – were a sign of how seriously the U.S. is treating Brunson’s case.

“The Turks were on notice that the clock had run out and it was time for Pastor Brunson to be returned and I hope they'll see this for what it is: a demonstration that we're very serious,” he told reporters.

"The Turks were on notice that the clock had run out and it was time for Pastor Brunson to be returned and I hope they'll see this for what it is: a demonstration that we're very serious." — Secretary of State Mike Pompeo

“We consider this one of the many issues that we have with the Turks,” Pompeo continued, but didn’t elaborate.

The U.S. government has been uneasy over Turkey’s military actions in Northern Syria and the plans to purchase an advanced air defense system from Russia.

“Brunson needs to come home as do all the Americans being held by the Turkish government,” he added. "Pretty straightforward. They've been holding these folks for a long time. These are innocent people.”

In terms of North Korea, Pompeo criticized the communist state for lagging behind on plans to honor the agreements made in Singapore during a summit in June between Kim Jong Un and President Trump.

The top diplomat said there was “still a ways to go before” achieving the goal of ridding the North of its nuclear weapons. As of now, the country is still in violation of numerous U.N. Security Council resolutions, Pompeo said.

"To the extent they are behaving in a manner inconsistent with that, they are in violation of one or both the UN Security Council resolutions, we can see we still have a ways to go to achieve the ultimate outcome we're looking for." — Secretary of State Mike Pompeo

“Chairman Kim made a commitment to denuclearize,” Pompeo told reporters. “The world demanded that [he] do so in the U.N. Security Council resolutions. To the extent they are behaving in a manner inconsistent with that, they are in violation of one or both the U.N. Security Council resolutions, we can see we still have a ways to go to achieve the ultimate outcome we're looking for.”

The remarks came after the White House said Thursday that Trump received a new letter from the North Korean leader in the wake of concerns that not enough progress has been made in getting rid of the nuclear weapons. Trump reportedly replied by letter to Kim.

The administration didn’t provide the contents of their letters, with White House spokeswoman Sarah Huckabee Sanders saying only that the letters addressed the commitment to work toward North Korea's “complete denuclearization.”

The Associated Press contributed to this report.