How can I understand this sentence?

How can I understand this sentence?

This is an article from a newspaper:
"The villagers' accounts all portray indiscriminate attacks against fleeing noncombatants, adding to a death toll that even in early estimates is high into the hundreds, and is probably vastly worse."

I can't understand this part:
What is the subject of is in "is high" and is in "is probably"?

Could you tell me, please?