On the eve of the second anniversary of Israel's 23-day offensive against Hamas in Gaza, a period of relative calm in the Israeli-Palestinian conflict has been shattered by missile launches from the coastal strip and Israeli counterstrikes.

On Monday and Tuesday, 15 mortars or rockets were fired from Gaza into southern Israel compared to some 200 for all of 2010, leaving one Israeli teenager lightly wounded and prompting a formal protest to the United Nations. Over the weekend, Israeli attacks killed four militants. Most of the missiles from Gaza have not been launched by Hamas forces, but Israel is holding the Islamist militant group responsible, and has started targeting Hamas positions for the first time in months.

While Gaza is still struggling to recover from the destruction of "Operation Cast Lead," the Israeli offensive that killed more than 1,400 Gazans, many observers worry that this unexpected flare-up in border violence could provoke another Israeli offensive.

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On Wednesday, Israeli Deputy Prime Minister Dan Meridor warned in an interview with Israeli Army Radio that continued rocket fire could prompt Israel to launch a new operation to quell the fresh round of missile attacks, which have been condemned by Palestinian Authority negotiator Saeb Erekat.

"Had Hamas wanted to break all the rules, it would have fired rockets at Herzliya or at Ben-Gurion Airport. It possesses the means and the capability," wrote Alex Fishman in the daily newspaper Yediot Ahronot. "But Hamas does not want to break all the rules. It just wants to test the limits and while doing so, to set new game rules."

The escalation is a test for Israeli Prime Minister Benjamin Netanyahu, who accused his predecessor Ehud Olmert of not responding forcefully enough to the hundreds of rockets from Gaza that preceded Operation Cast Lead.

Adding to the tension, Israeli military officials say that Gaza militants have armed themselves with Kornet missiles that can penetrate the armor of tanks.

Hamas has controlled Gaza since a violent takeover in June 2007. After declaring Gaza a "hostile" territory, Israel imposed an economic and military blockade on the strip. The economic blockade was partially relaxed following the international uproar over Israel's deadly intercept of a flotilla that challenged the blockade.

The fallout from that incident, in addition to diplomatic pressure over the stalled peace process, may give Mr. Netanyahu pause in how he deals with this recent flare-up in attacks, say analysts.

"Israel has to be very careful about how it handles Gaza," says Meir Javedanfar, a Middle East analyst based in Tel Aviv. "In light of Israel's increasing international isolation, any overreaction is going to be more difficult for Israel to gain support and sympathy from the US and European Union.''

There is a range of theories about what is behind the new violence. Those that assume Hamas has given militants more leverage to fire into Israel postulate that the organization is taking advantage of the impasse in peace negotiations.

Others suggest that Hamas does not have full control over the strip and that more extremist armed groups like Islamic Jihad and the Army of Islam are trying to foment a new round of attacks.

"Their authority in Gaza will be in danger in the case of any new war with Israel," says Nashat Aqtash, a communications professor at Birzeit University near Ramallah. "People are tired over the last four years. Hamas needs to things calm down."