The Israeli military said Gaza militants breached the truce and fired eight rockets at Israel and that in response, aircraft targeted multiple "rocket launchers and terror sites" across the enclave.
Hamas official Izzat Reshiq denied the Palestinians had breached the truce and denounced Israel's air strikes as "a violation of the calm".
No casualties were reported in any of the incidents and hostilities had ended by dawn yesterday.
A halt in more than a month of bloody fighting, in which 1,945 Palestinians and 67 Israelis have been killed, had been set to expire at midnight on Wednesday.
But at the last minute, the Palestinians announced in Cairo the truce had been extended by another five days for the sides to work out a long-term ceasefire, mediated by Egypt.
Bridging the gaps between Israel and the Palestinians in order to secure a permanent ceasefire has proven difficult.
Hamas and its allies want an end to the Israeli and Egyptian blockade on Gaza.
However, Israel and Egypt harbour deep security concerns about Hamas, the dominant Islamist group in the enclave.