Hundreds of civilians have been killed by ballistic missiles fired by the Syrian military into populated areas where it is battling rebels, the US-based Human Rights Watch group has said.

HRW said in a report released today that it has investigated nine apparent missile attacks that killed at least 215 people, half of them children, between February and July.

HRW activists visited seven of the nine attack sites. There were no apparent military targets near the inspected sites, the group said in a statement, calling on President Bashar Assad to stop indiscriminate attacks.

Government officials could not immediately be reached for comment.

The military has repeatedly denied it is targeting civilians during the two-year conflict, saying its troops are fighting "terrorists" hiding in civilian areas.