Armed opposition forces battled army troops on Tuesday as they advanced toward the city of Hama in central Syria, a war monitor said.“Hayat Tahrir al-Sham” (HTS) and its allies fought some of the “most violent” clashes with troops in the area since launching a lightning offensive last week, said the Syrian Observatory for Human Rights monitor.Since they launched their offensive last week, they have snatched swathes of territory from the Syrian government, including second city Aleppo.“Clashes have erupted in the northern Hama countryside, where [opposition] factions managed to seize several cities and towns in the last few hours,” said the Britain-based monitor, which has a network of sources inside Syria.For all the latest headlines follow our Google News channel online or via the app.“Syrian and Russian air forces carried out dozens of strikes on the area,” it added.Russia first intervened directly in Syria's war in 2015 with strikes on opposition-held area, and has pledged continued