More than 500 diplomats are expected to be present today when the fifth meeting over cluster bombs takes place at the Hotel Intercontinental.
Costa Rica holds the presidency temporarily of states that are parties to a treaty forbidding the use of cluster bombs, called in English the Convention on Cluster Munitions.
Cluster bombs are munitions that contain smaller bomblets that disperse over a wide area. Costa Rica said that 95 percent of the victims of such devices are civilians. Some 113 countries have signed the treaty, including Costa Rica, which supported the treaty from the start in 2008.
The United Kingdom has agreed to the terms of the treaty, but the United States has not.
U.S. military experts say there is some use for this type of munitions.
Supporters of the treaty say that many of the bomblets fail to explode and remain on the ground long after hostilities have ceased. These provide a danger to civilians, including children, they say.