BEIJING (Reuters) - North Korea kept a low profile at the opening of a summit in Beijing on China’s new Silk Road plan on Sunday, after the United States warned China Pyongyang’s attendance could affect the participation of other countries.

Kim Yong Jae, North Korea's minister of external economic relations, sits in a bus leaving the Belt and Road Forum in Beijing, China, May 14, 2017. Picture taken through a window. REUTERS/Thomas Peter

North Korea’s attendance at China’s biggest diplomatic event this year raised further eyebrows after Pyongyang fired a ballistic missile early on Sunday, in defiance of calls to rein in its weapons program.

North Korea’s delegation to the meeting on what China formally calls the Belt and Road initiative is being led by Kim Yong Jae, minister of external economic relations, according to the state run KCNA news agency, which has so far given no details of who he met or what he said.

A pool photograph of the opening ceremony at which Chinese President Xi Jinping delivered a keynote speech, showed Kim arriving together with White House adviser Matt Pottinger, the U.S. representative to the talks.

It is not clear if Kim or Pottinger spoke to each other.

It is also not clear which session of the summit the North Koreans were attending, and China has not given details of the attendees. There were about six afternoon sessions focusing on different areas from policy coordination and financial integration to think-tank exchanges.

One diplomatic source said they were probably in the trade session, attended by China’s commerce minister, while another said it could have been the policy session, attended by U.N. Secretary General Antonio Guterres.

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“I personally just wonder a bit whether in light of the whole background it sends the right signal to invite them to a meeting which is dedicated to peace and prosperity,” the European Union’s ambassador to China, Hans Dietmar Schweisgut, told Reuters on the sidelines of the Beijing summit.

U.S. WARNING

The U.S. embassy in Beijing had submitted a diplomatic note to China’s foreign ministry, saying that inviting North Korea sent the wrong message at a time when the world was trying to pressure Pyongyang over its repeated missile and nuclear tests, two sources with knowledge of the situation said.

Despite the warning, there was no evidence that North Korea’s presence at the summit, which runs until Monday, had affected participation.

Attending the forum, Italian Prime Minister Paolo Gentiloni, who is expected to discuss North Korea with other leaders of the G7 industrialized nations in Sicily later this month, said the international response needed to be diplomatic but firm.

“We don’t see these actions as whims or local eccentricity, it is a serious problem for international stability and security and I’m convinced that the G7 will contribute, in a friendly way, to resolving the issue,” Gentiloni told SkyTG24 television.

A member of the North Korean delegation declined to answer questions from journalists who approached him in a corridor during Sunday’s event.

China, which has been angered by North Korea’s repeated missile and nuclear tests, said on Saturday in reaction to the U.S. complaint that all were welcome at the Silk Road forum.

A South Korean official, speaking to Reuters on condition of anonymity, told Reuters on the sidelines of the forum that they had bumped into the North Korea delegation and expressed strong opposition to the missile test.

However, the official added that they felt North Korea “had an expectation” of starting dialogue with the new South Korean administration. He did not elaborate.

Park Byeong-seug, a veteran member of parliament and a senior official of new South Korean President Moon Jae-in’s liberal Democratic Party, is leading Seoul’s delegation.