WASHINGTON (Reuters) – U.S. President Donald Trump on Monday urged China on Monday to maintain a secure border with North Korea, pressing Beijing ahead of his anticipated meeting with North Korean leader Kim Jong Un next month aimed at denuclearization.

“China must continue to be strong & tight on the Border of North Korea until a deal is made. The word is that recently the Border has become much more porous and more has been filtering in. I want this to happen, and North Korea to be VERY successful, but only after signing!” Trump tweeted.

He did not elaborate on the significance of the North Korea-China border issue in any deal that might be reached on denuclearization. Trump has said his meeting with Kim will take place on June 12 in Singapore.

Pyongyang last week threatened to scrap any meeting if Washington continued to press for unilateral denuclearization.

In response, Trump said that as far as he knew, the meeting was still on track and sought to placate Kim by saying the North Korean leader would be protected as part of any deal.

Last week, Trump told reporters at the White House that the Kim was possibly being influenced by Beijing, North Korea’s main ally, after two recent visits he made to China.

(Reporting by Susan Heavey; Editing by Chizu Nomiyama and Frances Kerry)