Hamas official Ayman Taha said a truce was planned from 10pm UK time in a bid to end seven days of hostilities which claimed more than 120 lives.
There was no immediate Israeli comment but Prime Minister Benjamin Netanyahu said earlier he was open to a long-term deal to halt Palestinian rocket attacks on his country.
Egyptian President Mohamed Mursi, who has been brokering talks, had earlier announced "the farce of Israeli aggression against the Gaza Strip will end on Tuesday".
In the run-up to the ceasefire, Israel pressed on with air strikes and Palestinian rockets flashed across the border yesterday.
In the Gaza Strip, Hamas executed six alleged Israeli collaborators whom a security source said were caught red-handed filming military positions.
Militants chained one of the alleged spy's bodies to a motorbike and dragged it through the streets.
Israel's military targeted about 100 sites in Gaza yesterday including ammunition stores and the Gaza headquarters of the National Islamic Bank. Gaza's Hamas-run Health Ministry said six Palestinians were killed.
Israeli police said more than 150 rockets were fired from Gaza by late afternoon, many of them intercepted by Israel defences. Ten people were wounded in Israel.
Medical officials in Gaza said 126 Palestinians have died in a week of fighting, the majority of them civilians, including 27 children.
A longer-range rocket that targeted Jerusalem but fell harmlessly in the occupied West Bank triggered warning sirens in the city just as UN Secretary-General Ban Ki-moon Ban arrived in Jerusalem for truce discussions.
Mrs Clinton was heading to the region from Asia and is expected in Jerusalem for talks with Mr Netanyahu today.
The White House said President Barack Obama called Mr Mursi to discuss the conflict in Gaza and press for diplomacy to cool the violence, the third conversation he had with the Egyptian leader in roughly 24 hours.
Mr Mursi has warned Mr Netanyahu of serious consequences from an invasion of the kind that killed more than 1400 people in Gaza four years ago.
But he has been careful not to alienate Israel, with whom Egypt's former military rulers signed a peace treaty in 1979, or Washington, a major aid donor.
Addressing troops training in southern Israel, Defence Minister Ehud Barak said: "Hamas will not disappear but the memory of this experience will remain with it for a very long time and this is what will restore deterrence."
Hamas said four-year-old twin boys had died with their father when their house in the town of Beit Lahiya was struck from the air during the night.
The children's mother was critically wounded and neighbours said the occupants were not involved with militant groups.
Israel had no comment on the attack. It said it takes care to avoid civilians and accuses Hamas and other militant groups of endangering Gaza's 1.7 million people by placing rocket launchers among them.
l A man has been arrested after an armed attack on a security guard at the US Embassy in Tel Aviv. The guard, who suffered a leg injury, opened fire in the air during the attack and the suspect, who was wielding a knife and an axe, was held at the scene.