Palestinian militants in Gaza fired more than 50 mortar shells into Israel on Saturday, the heaviest barrage in two years, Israeli officials said, raising the prospect of a new Mideast flareup.

Also Saturday, Hamas police beat reporters and news photographers covering a rally in Gaza City, drawing a stiff condemnation from the reporters' association.

Israel invaded Gaza two years ago to put a stop to daily rocket barrages by Gaza militants, and Saturday's exchange showed how the conflict could quickly spiral out of control. Gaza's Hamas rulers are thought to be trying to avoid another Israeli invasion, after the last one caused widespread damage, killed more than 1,400 and left the territory under blockade, but Hamas claimed responsibility for some of the mortar rounds.

A Hamas official was killed and four civilians were wounded when Israel hit back with tank fire and air strikes, said Gaza Health Ministry spokesman Adham Abu Salmia.

Israeli police spokesman Tamir Avtabi said Gaza militants fired 54 mortar shells at Israeli border communities within 15 minutes. He said two Israeli civilians were lightly wounded by shrapnel, and residents were advised to stay at home or in bomb shelters.

Hayim Yellin, head of the Eshkol region where the mortars exploded, said they were the same type as those intercepted last week on a cargo ship loaded with weapons Israel said were sent by Iran to Palestinian militants in the Gaza Strip.

Israeli Foreign Minister Avigdor Lieberman said he will file a complaint at the U.N. after Saturday's unusually large barrage of rockets. In a statement, Lieberman said the Palestinians "primary goal is destroying Israel."

Footage broadcast on Israeli media showed homes pockmarked with large shrapnel holes from where mortar shells exploded.

Hamas spokesman Ismail Radwan said the shelling was in response to recent Israeli airstrikes that killed militants. He warned Israel "not to test Hamas' response."

Hamas displayed its control of Gaza in a violent manner Saturday, breaking up a demonstration favoring reconciliation between the Hamas government in Gaza and the Western-backed Palestinian Authority in the West Bank, headed by President Mahmoud Abbas. Hamas overran Gaza in 2007, leading to the split.

An Associated Press Television News cameraman was cornered by Hamas police and beaten with sticks. He was briefly detained and released unharmed. Other cameramen were beaten, and some had their equipment confiscated by Hamas.

Hamas also raided the offices of the Reuters news agency, CNN and Japanese channel NHK in Gaza. A Reuters producer was arrested by Hamas and witnesses later saw him leave hospital with a bandage wrapped around his hand.

Reuters Bureau Chief Crispian Balmer said, "A group of armed men entered our office in Gaza and threatened our employees and confiscated a video camera after we were spotted filming a demonstration from the building. They smashed a TV in the office, they clubbed one of our guys on the arm with a metal club and they threatened to throw another one of our employees out of the window."

The Foreign Press Association, which represents hundreds of journalists in Israel and the Palestinian territories, condemned the crackdown by Hamas security. "We demand that these tactics — which run counter to the rule of law and to the basic norms of legitimate government behavior — cease immediately," the FPA said in a statement. "Journalists must be allowed to their work safely and unhindered," the FPA said.

Hamas spokesman Sami Abu Zuhri sent a conciliatory message to reporters. "We condemn the attack on Reuters agency in Gaza and we call on the Hamas interior ministry to investigate this incident. We emphasize our respect for the media," he said.

The violence overshadowed a broadcast Saturday of an Abbas interview on an Israeli TV station. He told Channel 2 TV that he was "more determined than ever to reach a (peace) solution with Israel." Referring to reconciliation efforts with Hamas, he said, "Hamas has committed terrible crimes, but they are still part of the Palestinian people."