A deadly explosion targeting police has rocked a residential neighborhood in Damascus, killing up to 25 people. It's believed to have been a suicide bombing, with most of the casualties civilians. Syrian TV says the blast happened near a primary school. It comes as the leader of the country's biggest armed opposition group has reportedly called for President Assad's regime to be overthrown by military means. Meanwhile a former high-ranking army official who defected to the opposition has claimed the government was lying when it said the violence was caused by gangs aided from abroad. Author and Middle East expert Tariq Ali believes the opposition is responsible for the attack and they're laying the ground for a foreign intervention.