BEIRUT - Syrian activists say security forces have shot dead two people and launched a campaign of arrests just hours after the United States and its European allies demanded that President Bashar Assad leave office. The overnight shooting and arrests in different parts of the county came as the opposition called for more demonstrations following Friday noon prayers. The London-based Syrian Observatory for Human Rights and The Local Coordination Committees, a group that documents anti-regime protests, said one person was killed in a Damascus suburb. Another died early Friday in the central city of Homs. Human rights groups and witnesses say Syrian troops have killed more than 1,800 civilians since mid-March. A UN team has said Assad's crackdown “may amount to crimes against humanity.”