In a statement, the group also said the attack was in response to the arrest of 15 Palestinians, including Fatah members, by Israel in the West Bank on Monday.
One of the rockets exploded in an open field near the southern Israeli town of Sderot but caused no damage or casualties, an Israeli military spokeswoman said.
A second rocket backfired and landed in the Gaza Strip.
Palestinian armed groups had agreed to stop rocket attacks from Gaza in exchange for an end to Israeli military operations in the area.
David Chater, Al Jazeera's Jerusalem correspondent, said: "This is a shaky ceasefire... it has to be extended to the West Bank otherwise you will see continued responses which will undermine the chance for peace."
Security officers
Ehud Olmert, the Israeli prime minister, has said he hopes the truce can be extended to the West Bank.