US intelligence services have assessed that between 100 and 300 people died in the rocket explosion at a Gaza hospital earlier this week amid fighting between Israel and Hamas militants, a document seen Thursday by AFP said.

"We estimate the number of deaths is probably at the low end of the 100-to-300 spectrum," excerpts of the intelligence assessment provided to Congress said.

"We are still assessing the likely casualty figures and our assessment may evolve, but this death toll still reflects a staggering loss of life."

Hamas blames an Israeli airstrike but Israel says an errant Palestinian rocket caused the bloodshed Tuesday.