"Over the past day, arson balloons were launched from the Gaza Strip into Israeli territory," Israel's military said in a statement.

"In response... fighter jets struck military compounds and a rocket launch site belonging to the Hamas terror organisation."

AFP journalists in the Palestinian enclave also reported hearing explosions, which the army said hit sites in both Gaza City, and in Khan Yunis, in the south of Gaza.

The fire balloons and airstrikes are the latest violence testing a ceasefire between Israel and Gaza's Hamas rulers that came into place in May 21, ending 11 days of heavy fighting.

Palestinian militants in Gaza launched balloons for a third day running on Thursday, according to Israeli firefighters battling the blazes sparked by the devices.

After fire bombs sparked blazes on Tuesday, Israel's military launched a retaliatory wave of strikes early Wednesday, then launched a second round of strikes overnight Thursday to Friday.

The balloons are basic devices intended to set fire to farmland and bush surrounding the Gaza enclave.

Israel army chief Aviv Kohavi late Thursday issued orders to "increase the IDF's (Israeli Defense Forces) readiness and preparedness for a variety of scenarios including a resumption of hostilities," the army statement read.

"The IDF will continue to strike military capabilities and infrastructure belonging to the terror organisation and holds the Hamas as responsible for all events transpiring in the Gaza Strip," the statement added.