Concerned about the level of danger, Japan urges more countries to join the convention on cluster munitions.

Cluster bombs - designed to disperse large numbers of submunitions over a wide area - have been banned by many countries due to the risk of unexploded bombs causing civilian casualties.

In 2008, 123 countries signed the 2008 Oslo Convention - an international convention banning the production, stockpiling, trade and use of these weapons. However, the United States, Russia, Ukraine, China, India, Pakistan, Israel and South Korea have not signed.