Israeli aircraft targeted two Hamas sites in southern Gaza early Saturday, May 7 in response to a cross-border rocket attack, the army said, as tensions along the Palestinian territory's border simmered, AFP reports.

"Earlier today... a rocket was fired from the Gaza Strip at southern Israel," a military statement read. "In response... aircraft targeted two Hamas terror infrastructures in the southern Gaza Strip."

There were no immediate reports of casualties.

The rocket and air strikes marked the fourth day of the worst cross-border violence since the 50-day war in 2014, which left 2,251 Palestinians and 73 Israelis dead.

Mortar and tank fire between Israel and Palestinian militants, as well as Israeli air strikes, have raised concerns of a new war in the Hamas-run territory.

No Palestinian group immediately claimed responsibility for the rocket attack, but an Israeli military spokesman said Hamas, the Islamist rulers of Gaza, "must be held accountable" for it, AFP says.

Since Wednesday, Hamas and other militant groups have fired at least 12 mortar rounds across the frontier at Israeli forces conducting searches along the border and just inside Gaza for infiltration tunnels leading into southern Israel.