NEW : U.N. secretary-general accepts the U.N.-Arab League envoy 's resignation . Syrian rebels and the government agreed to a truce last week . On Monday , government troops fired upon an opposition neighborhood in Homs . The attack killed at least 10 people.
NEW : U.N. secretary-general accepts the U.N.-Arab League envoy 's resignation . Syrian rebels and the government agreed to a truce last week . On Monday , government troops fired upon an opposition neighborhood in Homs . On Tuesday , rebels shelled two pro-government neighborhoods in Aleppo , opposition says .