WASHINGTON, March 10 (Xinhua) -- U.S. President Donald Trump is open to a third summit with Kim Jong Un, top leader of the Democratic People's Republic of Korea (DPRK), National Security Adviser John Bolton said on Sunday.

In an interview with ABC on Sunday, Bolton said that President Trump had invested a lot of time in trying to develop a personal relationship with Kim, and Trump is confident in that relationship.

"He said he's open to a third summit, none has been scheduled, and some time they have to go by," Bolton added.

When asked about some reports on imagery analysis of activities in the DPRK, Bolton said that he would not speculate on what that particular commercial satellite picture shows.

Bolton also noted that Washington had not asked Pyongyang about the images of DPRK's rocket launch facility, while he revealed that he would speak with his South Korean counterpart on this matter Monday morning.

U.S. media widely reported that the DPRK appeared to have started "rapid rebuilding" of the long-range rocket site at Tongchang-ri Launch Facility, citing an imagery analysis from the Center for Strategic and International Studies, a Washington-based think tank.

"I would be very disappointed if that were happening. It's a very early report ... We'll take a look," Trump told reporters on Wednesday regarding the imagery analysis.

Bolton earlier said it was premature to make a judgment on the reports of the activities of DPRK rocket launch site.

Speaking on condition of anonymity, a senior State Department official on Thursday told the press that Tongchang-ri facility is "not a critical part" of DPRK's nuclear infrastructure at this point, and the United States has not "reached any specific conclusion" on those reports.

The official confirmed that Washington would seek clarifications on the purposes of those activities.

Trump and Kim Jong Un held their second summit in Hanoi, Vietnam on Feb. 27-28, without reaching an agreement.

Nevertheless, the White House said the two leaders had "very good and constructive meetings" and discussed various ways to "advance denuclearization and economic driven concepts."

Trump and Secretary of State Mike Pompeo also repeatedly expressed that Washington would continue the conversation with Pyongyang. Enditem