Mushir al-Masri, a Hamas MP, told Reuters: "In the face of this open war against the Arab and Muslim nations all options are open, including striking the depth of the Zionist entity."
Asked if that meant suicide bombings against Israelis, al-Masri said: "All options are open. Every means is allowed. This is a crime and state terror and a crossing of all red lines."
Shortly after Hamas issued its statement on Sunday, a rocket fired from Gaza hit the Israeli border town of Sderot.
Medics said a 29-year-old woman was wounded. Hamas's armed wing claimed responsibility for the launch.
Besides its offensive in Lebanon against Hezbollah, Israel has been engaged in an offensive against Palestinian fighters for more than a month since an Israeli soldier was abducted in a cross-border raid from Gaza.
The Palestinian prime minister called last week for the US to force Israel to end its offensive in the Gaza Strip. Condoleezza Rice, the US secretary of state, had refused to meet him.
"All that we ask the American administration is to take a moral stance towards the Palestinian people, and the Palestinian suffering and to bear its responsibility as a superpower in this world," Ismail Haniya said.
He called on America "to restrain the Israeli aggression and stop it".
"In Gaza, there is what resembles a real human catastrophe," Haniyeh said.