Israel’s military conducted a series of airstrikes that killed at least 25 Palestinians in the Gaza Strip after its forces came under fire, a fresh flare-up testing an already-fragile truce in the coastal enclave.

The strikes in Gaza City and southern areas of the strip are the second deadliest wave of Israeli attacks in the territory since the U.S.-backed ceasefire between Israel and Iran-backed Hamas took effect on Oct. 10.

Militants in southern Gaza’s Khan Younis had earlier in the day opened fire at Israeli soldiers, none of whom were injured, the Israel Defense Forces said. "In response, the IDF began striking Hamas terrorist targets across the Gaza Strip,” it said in a statement.