By Tom Perry BEIRUT (Reuters) - A Syrian rebel commander in the south vowed to wage guerrilla war against the Lebanese group Hezbollah and Syrian government forces which have launched a major offensive against insurgents in the sensitive border region near Israel and Jordan. The offensive that got under way this week is focused in an area south of Damascus that is the last **table foothold of the mainstream armed opposition to President Bashar al-Assad, who has consolidated control over much of western Syria. The Syrian Observatory for Human Rights, which tracks the war, says the push is being spearheaded by Hezbollah, and that government forces and allied militia have made significant progress. The Syrian army said on Wednesday that territory including four hills and three towns had been secured from insurgents it identified as members of the al Qaeda-linked Nusra Front.