Israeli tanks and aircraft struck militant positions in the Gaza Strip on Thursday soon after Palestinian militants fired mortar shells at an Israeli military post close to the territory, the Israeli army said.

A Reuters witness in Gaza said he saw smoke rising from at least two targets struck by Israel, one belonging to Hamas and another to Islamic Jihad militants. Witnesses in the southern Gaza Strip said two Islamic Jihad posts was hit there.

No casualties were reported initially on either side.

Israeli military spokesman Lieutenant-Colonel Jonathan Conricus said the militants’ mortar barrage was aimed the Israeli army post and at construction crews working close by on the Israeli side of the Gaza border.

Israel has been constructing a sensor-equipped underground wall along the 60-km (36-mile) Gaza border, aiming to complete the $1.1 billion project by mid-2019.

Conricus said Israel was not looking to escalate the situation but any further Israeli action would depend on what Gaza militants did. At least three rounds of airstrikes had taken place by dusk, the Reuters witness said.

“We remain ready with the tools necessary and the capabilities at hand should Hamas or the Islamic Jihad act aggressively again... We are not looking to escalate the situation or to initiate hostilities,” Conricus said.

The train service between the Israeli town of Sderot close the Gaza border and Ashkelon to the north was briefly suspended but resumed later in the evening.

The mortars were fired exactly a month after Israel blew up an attack tunnel that led from Gaza into Israeli in which 14 militants were killed.

Following the tunnel demolition, Islamic Jihad vowed to retaliate but Thursday’s action was their first significant reaction.

During the last Gaza war, in 2014, Hamas fighters used dozens of tunnels to blindside Israel’s superior forces and threaten civilian communities near the frontier, a counterpoint to the Iron Dome anti-missile system that largely protected the country’s heartland from militant rocket barrages.

Israel and the United States have called for Hamas to be disarmed as part of the pact between it and the Palestinian Authority, so Israeli peace efforts with Palestinian President Mahmoud Abbas, which collapsed in 2014, could proceed. Hamas has rejected the demand.

On Wednesday, Abbas’s Fatah and Hamas agreed to delay the final transfer of power of Gaza from Hamas to the Western-backed Palestinian government by 10 days to Dec. 10 to allow time to complete arrangements, officials said.