US President George W. Bush on Friday branded the Hamas rocket attacks on Israel an "act of terror" and outlined his own condition for a cease-fire in Gaza, saying no peace deal would be acceptable without monitoring to halt the flow of smuggled weapons to terrorist groups. Bush chose his taped, weekly radio address to speak for the first time about Israel's military assault targeting Hamas in the Gaza Strip, which began last Saturday. "The United States is leading diplomatic efforts to achieve a meaningful cease-fire that is fully respected," Bush said. "Another one-way cease-fire that leads to rocket attacks on Israel is not acceptable. And promises from Hamas will not suffice - there must be monitoring mechanisms in place to help ensure that smuggling of weapons to terrorist groups in Gaza comes to an end." The White House released Bush's radio address one day early. It airs on Saturday morning. More than 400 Palestinians and four Israelis have been killed in the latest offensive. The UN estimated Friday that a quarter of the Palestinians killed were civilians. Bush also expressed deep concern about the humanitarian suffering of the Palestinian people in Gaza, and blamed Hamas for the situation. "By spending its resources on rocket launchers instead of roads and schools, Hamas has demonstrated that it has no intention of serving the Palestinian people," Bush said. "America has helped by providing tens of millions of dollars in humanitarian aid, and this week we contributed an additional $85 million through the United Nations. We have consistently called on all in the region to ensure that assistance reaches those in need." The White House has cautiously said Israel must be mindful of the toll its military strikes will have on civilians. Here, too, Bush blamed Hamas for hiding within the civilian population. "Regrettably, Palestinian civilians have been killed in recent days," he said. Bush offered no criticism of Israel, depicting the country's air assaults as a response to the attacks on its people. The White House will not comment on whether it views the Israeli response as proportionate or not to the scope of rockets attacks on Israel. "This recent outburst of violence was instigated by Hamas - a Palestinian terrorist group supported by Iran and Syria that calls for Israel's destruction," Bush said. "Eighteen months ago, Hamas took over the Gaza Strip in a coup, and since then has imported thousands of guns and rockets and mortars. Egypt brokered a cease-fire between Hamas and Israel, but Hamas routinely violated that cease-fire by launching rockets into Israel." The president said that Hamas ultimately ended the cease-fire altogether on Dec. 19 and "soon unleashed a barrage of rockets and mortars that deliberately targeted innocent Israelis - an act of terror that is opposed by the legitimate leader of the Palestinian people, President (Mahmoud) Abbas." In their waning days in power, Bush and Secretary of State Condoleezza Rice have been working the phones with world allies to try organize a truce. International calls for a cease-fire have been growing. Increasingly, the conflict appears to be another one that President-elect Barack Obama will inherit when he takes office in Jan. 20. Rice on Friday briefed Bush on developments in Gaza but said she had no plans to make an emergency visit to the region. Bush promised to stay engaged with US partners in the Middle East and Europe and to keep Obama updated.