"Since assuming leadership in North Korea, Kim Jong-un averaged 10.8 missile tests per year in the 2012-2016 period. Though, these numbers are driven up by the higher volume of tests in recent years," he said in an article posted on the KEI's The Peninsula website.

In 2012 and 2013, North Korea conducted a total of eight missile tests, the expert said. If those initial years are excluded and only the more recent period where the rate of testing has increased are examined, the average is 15.3 tests per year in the 2014-2016 period, he said.

Since South Korea's new President Moon Jae-in took office last month, the North has conducted five missile tests, but the rate is not unprecedented, the expert said, noting that Pyongyang carried out seven tests, for example, in a four-week time period in 2014.

The average number of North Korean missile tests per month was 0.25 in 2012, 0.42 in 2013, 1.3 in 2014, 0.83 in 2015, 1.7 in 2016 and 1.8 in 2017, the expert said.

"If North Korean tests continue at the same pace as they have so far this year, we should expect a new missile test every 2.1 weeks and another 13-14 tests. If that is the case, which it may not be, North Korea would exceed last year's total number of missile tests by 3-4 tests," Stangarone said.

"The international community should be prepared to more quickly respond to the advancing pace of North Korea's missile tests by preparing a menu of tightening multilateral sanctions options that have been informally agreed to in advance," he said. (Yonhap)