The Israeli military struck the Gaza Strip early Monday, hours after a rocket was shot into southern Israel as intense cross-border fighting persisted for a third straight day.

The army said it attacked “underground infrastructure” in the southern Gaza Strip, likely referring to a tunnel dug by the Hamas terror group and others in the Palestinian enclave.

The military did not say if the strikes were from tank shelling or airstrikes.

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The Palestinian Safa news site reported that heavy damage was caused by 10 airstrikes, but no injuries were reported.

Palestinians in the Strip reported hearing explosions near agricultural areas outside Rafah in the south of the Strip on social media.

أصوات القذائف والصواريخ التي سقطت شرق رفح جنوب قطاع #غزة ,, حيث استيقظ الاطفال والنساء من النوم نتيجة الأصوات العالية والتي تسبب بخوفهم , ننوه بأن طيران الاحتلال ما زال يحلق بكثافة في سماء القطاع . pic.twitter.com/RNOJswLt4Y — غزة الآن – Gaza Now (@gazalnps) February 19, 2018

The IDF said the attack was in response to a projectile fired at Israel earlier. The rocket, fired late Sunday, reportedly landed in an open area in the Sha’ar Hanegev region bordering the Strip.

There was no immediate claim of responsibility for the rocket, but Israel maintains a policy of holding Hamas, which rules Gaza, responsible.

“Hamas is responsible for anything that happens in the Strip and whatever comes out of it, both over and underground,” the army said in a statement.

Israel has been working to thwart tunnels being dug by Hamas and other group under the Strip, some of which cross into Israeli territory and are thought planned for use in future attacks. The Defense Ministry is at work on an underground barrier that it says will stop the tunnels from crossing into Israel.

Fighting with Gaza ramped up over the weekend after four soldiers were injured by an explosive device attached to a flag on the border. Later Saturday, a house in the community of Sha’ar Hanegev sustained damage from a rocket fired from Gaza. No injuries were reported.

Israel responded by targeting 18 sites in Gaza, including Hamas posts and one target that the army said was managed by the Palestinian Islamic Jihad group, thought behind the IED.

The targets included observation posts, an attack tunnel and Hamas weapons factories, the army said.

Two Palestinians were killed, according to the Hamas-run Gazan health ministry.