The scheduled talks between South Korean President Moon Jae-in and Abu Dhabi Crown Prince Mohammed bin Zayed Al-Nahyan were canceled due to an "unforeseen matter of state" of the de facto ruler of the United Arab Emirates (UAE), a senior Seoul official has said.

Moon, who is in Dubai for a three-day visit as part of his weeklong trip to the Middle East, had been scheduled to hold talks with the Abu Dhabi crown prince Monday, but the talks were called off as the UAE side "politely asked for understanding for an unforeseen and urgent matter of state," the official said on the condition of anonymity Sunday.

It was not immediately clear why the talks were canceled. Moon had planned to deliver a keynote address on carbon neutrality at the Abu Dhabi Sustainability Week in Abu Dhabi on Monday and hold talks with the Abu Dhabi crown prince on ways to deepen bilateral cooperation over climate change, national security and defense, and public health.

Asked whether the cancellation was related to the COVID-19 situation in the UAE, the official replied that the UAE side did not give the exact reason for the cancellation.

On Sunday, South Korea signed a preliminary deal with the UAE to sell Seoul's midrange surface-to-air missiles to the Persian Gulf nation, in the latest sign of deepening defense cooperation between the two nations.

The deal was signed after Moon held talks with UAE Prime Minister Sheikh Mohammed bin Rashid Al Maktoum in Dubai, Seoul's presidential office said without providing further details, including the value of the memorandum of understanding.

But media reports have indicated that the deal is likely to reach $3.5 billion.

Last November, the UAE's defense ministry announced that it plans to acquire the missiles.

The M-SAM system, called Cheongung II, is a core element of South Korea's multilayered anti-missile program. Cheongung, means heaven's bow in Korean. Employing "hit-to-kill" technology, the missile is designed to intercept hostile missiles coming in at altitudes below 40 kilometers.

Since 2011, South Korean troops of the Akh unit, which means "brother" in Arabic, have been on a mission in the UAE to train the nation's service members and protect Korean nationals in emergencies.

Kang Eun-ho, head of South Korea's Defense Acquisition Program Administration, told reporters that the deal marked Korea's biggest deal for exports of a single weapon, but he declined to reveal the value of the deal, citing the sensitivity of the issue.

When asked whether his agency has been in talks with other nations to sell the M-SAM system, Kang replied, "Yes."

The UAE is the first leg of Moon's three-nation trip to the Middle East that will also take him to Saudi Arabia, as well as Egypt.

Moon will visit Riyadh on Tuesday and hold talks with Saudi Arabia's de facto ruler Crown Prince Mohammed bin Salman. (Yonhap)