"IDF (Israel Defense Forces) fighter jets and attack helicopter struck an underground infrastructure belonging to the Hamas terror organization in the southern Gaza Strip" following the rocket attack, the military said in a statement.

Palestinian security sources said the aircraft hit two targets in Khan Yunis and Deir al-Balah belonging to Hamas, the Islamist movement hostile to Israel that has held power in Gaza since 2007.

The IDF had earlier said that the rocket fired from the Khan Yunis area "was intercepted by the Iron Dome" aerial defence system, without indicating if it had caused any casualties or damage.

There was no immediate claim of responsibility.

Several hours before the exchange of fire, the Israeli army announced it had found on Tuesday a tunnel that crossed "dozens of meters (yards) into Israel from Gaza".

Army spokesman Jonathan Conricus said the tunnel was a violation of Israel's sovereignty.

He said Israel did not know who had dug the tunnel, but said it held Hamas responsible for all activity in the Palestinian enclave.

The tunnel was discovered thanks to underground sensors near the border, the army statement said, adding that "there was no threat to nearby Israeli communities".

Prime Minister Benjamin Netanyahu said in a statement that Israel would "continue to take determined action... against any attempt to attack our sovereignty or our citizens."

Authorities have discovered some 20 tunnels originating from Gaza since 2014, Conricus said.

In August, militants in the Gaza Strip launched a string of incendiary balloons and rocket attacks toward Israel, which responded with air strikes on the enclave.

Hamas and Israel reached an agreement at the end of the month to cease hostilities, although attacks continued.

The deal, mediated by Qatar, aimed to put back on track a fragile Egyptian-brokered truce.

The last reported rocket attack from Gaza was on October 16.

Israel has fought three wars with Hamas since 2008 and there have been numerous flare-ups.

The impoverished and densely populated Gaza Strip has been under a crippling Israeli blockade since 2007, after Hamas took over the coastal enclave.