GAZA CITY, Gaza Strip — Israeli airstrikes struck more than 20 targets Saturday in the Gaza Strip as militant rocket fire continued toward Israel following the collapse of a three-day truce aimed at ending the war between Israel and Hamas.

The Islamic militants resumed their rocket attacks Friday shortly before the 72-hour truce expired, drawing a wave of retaliatory airstrikes that killed at least five Palestinians. The fighting shattered a brief calm in the monthlong war and dealt a blow to Egyptian-led efforts to secure a long-term cease-fire between the bitter enemies.

Hamas officials said the Israel airstrikes Saturday hit houses, mosques, its warehouses and training sites. A handful of rockets landed Saturday morning in Israel.

More than 1,900 Gazans have been killed in the four-week war, roughly three-quarters of them civilians, according to Palestinian and United Nations officials. Israel disputes that breakdown, saying more militants have been killed. Sixty-seven people have been killed on the Israeli side, including three civilians.

The war grew out of the killing of three Israeli teens in the West Bank in June. Israel blamed the killings on Hamas and launched a massive arrest campaign, rounding up hundreds of its members in the West Bank, as Hamas and other militants unleashed rocket fire from Gaza.

On July 8, Israel launched an air campaign on the coastal territory, sending in ground troops nine days later to target rocket launchers and cross-border tunnels built by Hamas for attacks inside Israel.

Hamas, which violently seized control of Gaza in 2007, rejected several cease-fire offers throughout the fighting. Its primary demand is the lifting of an Israeli-Egyptian blockade imposed after they seized power.