Senior officials from about 5 of the world's top intelligence services held a secret meeting on the sidelines of the Shangri-La Security Dialogue in Singapore earlier this week, five people said.

They told Reuters the meetings were organised by the Singapore government and held secretly in a separate venue alongside the security summit several years ago. These meetings have not been previously disclosed.

According to the agency, US Director of National Intelligence Avril Haines participated in the secret meeting representing the United States, while China was among the other countries present, despite the state of tension between the two major powers.

An Indian source said Samant Joel, director of India's intelligence service, the research and analysis wing, also attended the meeting.

A person familiar with the discussions said: "The meeting is an important element of the international shadow agenda. Looking at the group of countries involved, this is not an intelligence meeting but rather a means of promoting a deeper understanding of intentions and insiders."

"There is an unspoken code among the intelligence services that they can speak when there is difficulty in communicating and dealing diplomatically. "It's a very important factor during times of stress and the Singapore meeting helps reinforce that."

The five sources who discussed the meetings declined to be identified because of the sensitivity of the matter, but a spokesman for Singapore's defence ministry said that while attending the Shangri-La Security Dialogue, "participants, including senior officials from intelligence agencies, take the opportunity to meet with their counterparts".

"Singapore's Ministry of Defence may facilitate some of these bilateral or multilateral meetings. Participants consider such meetings held on the sidelines of (dialogue) useful."

The U.S. Embassy in Singapore said it had no information about the meeting. The Chinese and Indian governments did not immediately respond to requests for comment.

The person familiar with the meetings said that although few details were available, the issues of war in Ukraine and cross-border crimes emerged during those talks on Friday. The heads of the intelligence services held an informal meeting on Thursday evening.

One of the sources said no representative of Russia attended. Ukrainian Deputy Defense Minister Volodymyr H. Havrilov attended the Shangri-La dialogue, but said he did not attend the intelligence services' meeting.

The Shangri-La Dialogue, which attracts participation from senior defence officials, military leaders, diplomats, arms manufacturers and security analysts from around the world, will be held in Singapore from June 600 to 49, with <> delegates from <> countries in attendance.

Analysts say the dialogue is crucial given the number of bilateral and multilateral military meetings held on its sidelines, as well as dialogue sessions and speeches by defense ministers.