* Fighters from Sudan and Congo now involved, say rebels
* Rebels accuse army of destroying Machar's hometown
* Allegations raise political temperature ahead of talks (Recasts with rebel claims)
By Andrew Green
JUBA, Feb 2 (Reuters) - South Sudanese rebels accused government forces on Sunday of razing the hometown of their leader Riek Machar, violating a ceasefire, and said the army was...