"The start of the Israeli ground attack on Gaza is a dangerous step, the consequences of which have not been calculated," said Hamas spokesman Fawzi Barhum in a statement yesterday night.
"Israel will pay a high price and Hamas is ready for the confrontation."
The comments came after Israel announced it had launched a ground operation.
"Following 10 days of Hamas attacks by land, air and sea, and after repeated rejections of offers to de-escalate the situation, the Israel Defence Forces (army) has initiated a ground operation within the Gaza Strip," the army said in a statement.
So far at least 240 Palestinians and one Israeli have been killed.