Al Jazeera reports Syrian troops have advanced inside and near northern Aleppo in what appears to be an attempt to lay siege to rebel-held parts of the country's largest city, activist say. Rami Abdurrahman, who heads the Britain-based Syrian Observatory for Human Rights, said on Monday that reinforcements, including members of Iran's elite Republican Guards and allies from Lebanon's Hezbollah group, had recently arrived in Aleppo. "The latest attack does not mean that Aleppo will fall. It is going to be a very difficult battle,'' he said. If successful, the government forces' advance would be the biggest blow to the opposition since they entered the northern city two years ago.