Port calls by North Korean ships fell sharply in March after a revised law requiring vessels be insured against oil pollution took effect on March 1.

Officials of the Land, Infrastructure and Transport Ministry said Tuesday that North Korean ships made 29 calls in March, down from 115 the previous year. Overall port calls by foreign ships last month reached 9,120, compared with 9,820 the year before.

The revised law effectively serves as an economic sanction on North Korea.