An explosion was heard in Gaza City, where smoke billowed from the seventh floor of a high-rise building. It was not clear what the target of the attack was. Israel closed roads around Gaza earlier this week and sent reinforcements to the border as it prepared for a retaliatory attack after the arrest of a senior member of the Islamic Jihad militant group in the occupied West Bank on Monday. It was not immediately clear what Israel was targeting or how much the situation would escalate. Israel and the militant group Hamas have fought four wars and several smaller skirmishes in the 15 years since the latter seized power from rival Palestinian forces. Israeli Defense Minister Benny Gantz visited communities near Gaza on Friday, saying authorities were preparing “actions to remove the threat from this area,” without elaborating. “We will operate with internal resilience and external strength to restore routine life in southern Israel,” he said, “We do not seek conflict, however we will not hesitate to defend our citizens if necessary.” The latest escalation began when Israeli forces arrested a senior member of the Islamic Jihad militant group in the West Bank city of Jenin late on Monday. A teenage member of the group was killed in fighting between Israeli troops and Palestinian militants. Ahmed Mudalal, an Islamic Jihad official in Gaza, said the group had made demands from Israel through Egyptian mediators, including the release of the detained militant and another captive, an end to raids on the West Bank and the lifting of the blockade of Gaza . He said he has yet to receive a response. Earlier on Friday, several hundred Israelis demonstrated near the Gaza Strip to demand the return of a captured Israeli citizen and the remains of two Israeli soldiers held by Hamas. Supporters of Israeli soldiers Hadar Goldin and Oron Shaul, who were killed during the 2014 war in Gaza, and captured Israeli civilian Avera Mengistu, protest on Friday. Photo: Ariel Schalit/AP The protesters were led by the family of Hadar Goldin, who along with Oron Shaul were killed in the Gaza war in 2014. Hamas still holds their remains, as well as two Israeli citizens who were adrift in Gaza and believed to be mentally ill. hoping to exchange them for some of the thousands of Palestinian prisoners held by Israel. They held a large sign demanding the return of the remains of the soldiers as well as Abraham Mengistu, an Israeli of Ethiopian descent in his late 20s or early 30s. Mengistu’s family participated in the protest. Israel and Egypt have maintained a strict blockade on the territory since Hamas seized control of Gaza. Israel says the shutdown is necessary to prevent Hamas from developing its military capabilities, while critics say the policy amounts to collective punishment of Gaza’s 2 million Palestinian residents. Israel says no major moves to lift the blockade can be made until the soldiers’ remains and captured civilians are released. Israel and Hamas have held several rounds of Egyptian-brokered talks on a possible swap.