VIDEO - Israeli army helicopters fired missiles Wednesday afternoon at a Hamas building in the southern Gaza Strip, killing four members of the Islamic group and wounding 20 others. The army said the building situated in Rafah along the border with Egypt was used by Hamas to plan terror attacks. Several hours later, Palestinian sources in northern Gaza said an Israeli aircraft fired at armed gunmen near Jabaliya. It remains unclear if there were any casualties in the attack and the factional affiliation of the gunmen is unknown. The Wednesday afternoon attack is the first of its kind since the truce between Israel and the Palestinians was declared in November 2006. Up until now, the army has refrained from attacking command posts and only operated against Qassam cells. IDF officials said that the strike was the result of consultations with the defense minister Wednesday. According to the Palestinians, the strike would torpedo understandings reached between Palestinian Authority President Mahmoud Abbas and Hamas' political chief Khaled Mashaal regarding a ceasefire between the two organizations. The IDF's Spokesperson Unit said in response, "Following the ongoing terror attacks of Hamas and the terror organizations against the State of Israel, the IDF attacked a Hamas command post in Rafah in a joint operation of the Central Command and the Israel Air Force. "The IDF will continue to operate against the terror groups in order to provide security for the people of Israel." Earlier Wednesday, Israeli helicopters fired at open fields in the northern Gaza Strip used by gunmen to fire rockets towards Israel. No injuries were reported. Prime Minister Ehud Olmert will hold a security meeting in his office Wednesday afternoon to discuss the escalation in rocket attacks from Gaza. The meeting will be attended by the defense minister, the army chief, the head of the Shin Bet and other senior IDF officials.