The Israeli army on Wednesday intensified its offensive on the Hamas-run Gaza Strip, striking Hamas sites and killing at least 14 people on the second day of a military operation it says is aimed at quelling rocket fire against Israel.

Hamas is broke. It's lost some of its biggest supporters. Its supply lines from Egypt are cut off. The Islamist militant group is at one of its weakest points since it was founded in 1987. Yet, its operatives are busy firing rockets at Israel, as hostilities between the two arch-enemies continues to escalate.

Why? Hamas has little other choice but to fight, say observers here.

"Look, Hamas [is] in trouble, but there is no way it's going to stop the military campaign against Israel, because the organization doesn't see a good way to get out of it," said Shaul Mishal, one of Israel's foremost experts on Hamas.

An Iron Dome launcher fires an interceptor rocket in the southern Israeli city of Ashdod. (Baz Ratner/Reuters)

Just yesterday, Hamas vowed that all Israelis are targets, following an Israeli airstrike on the Gaza of one of the leaders of its militant wing.

Israel says it has killed other Hamas members because they were involved in firing rockets at its territory.

"The occupation started this aggression, and it must pay the price," Fawzi Barhoum, a Hamas spokesman, said on Facebook. "We will be the ones to define the cost of the bill."

Hamas has claimed responsibility for rockets fired on Jerusalem and the northern Israeli city of Haifa. Almost all of the rockets fired by Hamas and other militant groups in Gaza have either been destroyed by Israel's Iron Dome defence shield, or fallen in open areas. There have been few reports of damage and casualties on the Israeli side.

Yet the screeching air raid sirens that have caused fear and panic in southern Israel for years now are creeping north. Residents of Tel Aviv once thought themselves immune to attacks from Gaza.

Further escalation

Now, Hamas and Islamic Jihad, among others, are capable of launching rockets that experts say can travel up to 120 kilometres, much farther north of Tel Aviv.

Israeli leaders continue to warn Hamas it faces a further escalation in Gaza, if the rocket fire doesn't stop. Israel's defence ministry has authorized the call-up of 40,000 reserve troops for a potential ground invasion of Gaza.

After two days of punishing airstrikes by Israel's air force, however, is Hamas preparing to back down?

The militant group still controls Gaza, but it no longer governs the coastal enclave. It joined a unity government with its West Bank rival Fatah last month. It's thought the Hamas leadership was actively working to improve its relationship with Fatah, but that fell apart when three Israeli teenagers were kidnapped in the West Bank last month. Their bodies were discovered last week.

While Hamas denied involvement in the abductions — even though Israel's Prime Minister Benjamin Netanyahu placed the blame squarely on Hamas — Khaled Meshal, Hamas's political chief, praised "the hands that carried out the kidnapping of the settlers."

Cairo sees Hamas as an enemy

The ouster of Egypt's Muslim Brotherhood president a year ago has had a dramatic effect on Hamas. The army-controlled government in Cairo sees Hamas as an enemy, and has cut off smuggling tunnels that were vital for the militant group to move supplies and weapons into Gaza.

The economy in the coastal enclave is in crisis. With financial support from Qatar drying up, Hamas is broke. It's been unable to pay thousands of civil servants.

So how long can it keep this rocket campaign against Israel?

Mishal, a professor with one of Israel's foremost academic institutions, IDC Herzliya, has a prediction:

"I think it will take another few days, maybe even more, until both sides will reach the point of mutual dissatisfaction, which means they will realize there is no way to continue, because both of them are going to lose rather than to win."