(CBS News) DAMASCUS - One of the best-known armed Syrian opposition groups, the Free Syrian Army, has said it will no longer respect the terms of the Kofi Annan-brokered ceasefire, the latest sign that Syria is slipping into all-out civil war.
"We have decided to end our commitment," spokesman Major Sami al-Kurdi told the Associated Press. "We have resumed our attacks but we are doing defensive attacks, which means we are only attacking checkpoints in the cities."
At a meeting in Istanbul, meanwhile, a member of a newly established group - The Syrian Revolutionaries Front - called for attacks on the capital. Sheikh Salem Abulaziz al Mussalat said the time had come to start focusing military efforts on Damascus.
Certainly opposition activist video posted online in the past few days show an uptick in the number of well-organized attacks on Syrian soldiers, their tanks and their armored vehicles.
Rebel groups claim to have killed between 80 and 100 soldiers in the past few days alone - the majority of them in the northern Idlib province. If those numbers are accurate, it amounts to some of the heaviest losses of government troops since the uprising began in March of 2011.
It is not clear what effect the opposition fighters' rejection of the ceasefire will have on the dozens of U.N. military observers who have been working inside the country, especially if the violence escalates dramatically. So far, the U.N. observer mission has refused to comment.
The U.N. did say Tuesday, however, that the regime of President Bashar Assad had agreed - in writing - to a deal to let the global body's multiple humanitarian agencies, and some non-governmental organizations, access four areas which have seen significant violence.
"Whether this is a breakthrough or not will be measured in the coming weeks," John Ging of the U.N. Office for the Coordination of Humanitarian Affairs said in Geneva after a closed-door session to discuss the situation in Syria.
The areas covered under the agreement are Daraa, Deir el-Zour, Homs and Idlib, and they should be open to aid workers ferrying in desperately-needed medical supplies and provisions within days, said Ging.
CBS News accompanied two jeeps full of observers Tuesday to Douma, a Damascus suburb that has been heavily shelled by the Syrian military over the past months, though it was calm Tuesday.
Syrian high school students are taking their final exams this week, and the schools in Douma appeared to be working normally. However, local people report that shooting often breaks out in the evening and lasts all night.
Most businesses and shops were closed - part of a widespread strike by merchants that began after the massacre in Houla last week.
On Tuesday morning, meanwhile, the Syrian government announced it was expelling foreign diplomats from the country, including the ambassadors of the United States, Britain, Turkey and France in an apparent tit-for-tat move after the expulsion of Syrian diplomats from several Western capitals last week.