UN chief Ban Ki-moon says the Arab League plans to revive its mission to Syria, and has sought help from the UN.Mr Ban said the "disastrous” failure to agree a UN resolution on Syria had encouraged Damascus "to step up its war on its own people”.The international community is struggling to find a way forward in the crisis after Russia and China blocked the resolution last week.Syrian forces are continuing to attack opposition strongholds in the country.Activists say shelling resumed early on Thursday in the central city of Homs - where the army launched an assault last week.With several districts controlled by rebel forces - including many army defectors - Syria’s third-largest city has become a major focus of unrest against President Bashar al-Assad.More than 50 people were killed there on Wednesday alone, according to the UK-based Syrian Observatory for Human Rights.Speaking at the UN, Mr Ban said: "I fear that the appalling brutality we are witnessing in Homs, with heavy weapons firing into civilian neighbourhoods, is a grim harbinger of worse to come.”He said Arab League chief Nabil el-Arabi had told him he intended to revive a monitoring mission in Syria, which collapsed last month amid escalating violence.Mr Ban said Mr Arabi had asked for UN help with the project and proposed a joint UN-Arab League observer mission, including a joint special envoy.