TOKYO — North Korea’s acting ambassador to Italy disappeared from the embassy in Rome in November, apparently in a defection attempt, according to a South Korean lawmaker briefed by intelligence officials.

The potentially embarrassing news for Kim Jong-un, North Korea’s leader, came just two days after he extolled his country’s economic and diplomatic progress and delivered an implied threat that if international sanctions against the North continued, he would “have no choice” but to return to nuclear confrontation.

Little is known about what happened to Cho Seong-gil, who had been North Korea’s acting ambassador to Italy since October 2017. If his defection is confirmed, he would be the highest-ranking defector since Kim Jong-un became leader in 2011. In 2016, the No. 2 diplomat in Britain, Thae Yong-ho, defected to South Korea, expressing disillusionment with Mr. Kim’s government.

According to Kim Min-ki, a lawmaker in the party of President Moon Jae-in of South Korea, Mr. Cho and his wife fled the North Korean Embassy and residence in Rome and have been in hiding since early November, about a month before his term there was due to end.