Last week, Trump met with the highest ranking North Korean official in 18 years at the White House.
"We feel like things are continuing to move forward and good progress has been made", Ms Sanders said.
The former New York City mayor told The Wall Street Journal that Trump's cancellation of the meeting, which is now back on for the planned date of June 12, forced the North Korean leader into a favorable position.
Experts have voiced concern that despite Trump's claim to be the world's greatest dealmaker, he knows little about North Korea, arms control or global diplomacy.
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Ragland, a yoga instructor, met Queen Elizabeth II for tea with Harry and Markle at Windsor castle a day before the wedding. This isn't the first time the Queen has given such a generous wedding gift.
Vivian Balakrishnan will pay the official visit to the North Korean capital at the invitation of the North's Foreign Minister Ri Yong Ho, Singapore's foreign ministry said in a statement.
At the back are the national flowers of both countries - roses for the United States and magnolias for North Korea - and a dove with the words "world peace". It said that the White House press corps usually numbers between 50 and 100 for overseas trips.
"We're not paying for their expenses", she said.
In a letter to Trump earlier this week, several Democratic lawmakers said that they would not support an agreement with North Korea unless its provisions included the complete disarmament of Pyongyang's nuclear and ballistic missile programs.
He "could even play some sort of role in the negotiations" between Donald Trump and Kim Jong Un, which would make for the latest twist in talks between the two countries. My prediction is that at some point during this process, if I were the North Koreans, I'd want to extend this.
"We've reached a point where the summit is extremely fragile and can easily be tipped out of balance", Graham Ong-Webb, a research fellow at Singapore's S. Rajaratnam School of International Studies, told AFP.