Tensions between Israel and Palestinians in the Gaza Strip rose into the night Friday, as both sides fired back-and-forth in the wake of a deadly terrorist attack Thursday.

By midnight, three more Palestinians had been killed in an Israeli airstrike, bringing the total to twelve. Palestinians responded by firing 30 Grad and Qassam rockets around southern Israel, injuring six people.

Israel said bombers targeted the militants responsible for the Thursday attack that killed eight Israelis near the country's southern most city, Eilat.

Around noon on Thursday, a group of heavily armed gunmen attacked a bus and civilian cars on a highway, opening fire and detonating a road-side explosive.

The Israel Defense Forces will not tolerate any attempt to harm Israeli citizens and IDF soldiers and will continue to operate resolutely against anyone who terrorizes Israel, the I.D.F. said in a statement. The Hamas terrorist organization is the address, and it bears the responsibility.

But, along with those suspected to be responsible, a number of civilians were killed in Gaza, including a three-year-old boy, medical services spokesman Adham Abu Selmia said, according to Xinhua.

The militants entered Israel from the southern border with Egypt. According to a new report from Egypt, four Egyptian soldiers and one policeman were killed by Israeli soldiers. Egyptian officials shouted invectives at their Mid-East neighbors, a further sign that Israel-Egypt relations are not as peaceful as they were under ousted President Hosni Mubarak.

So far, Israel has officially remained mum on the event, but they say they are investigating the death of the Egyptians.

There was an exchange of fire between Israeli soldiers and terrorists on the Egyptian border following the deadly terror attack Thursday morning. We are investigating this matter thoroughly and will update the Egyptians, the Israeli military said.

But, according to an Israeli officer, it was a suicide bomber, and not Israeli soldiers, that killed the Egyptians.

Israel and any other [country] must understand that the day our sons get killed without a strong and an appropriate response, is gone and will not come back, tweeted Amr Moussa, former Arab League chief. The blood of our martyrs which was spilled while carrying out their duties, will not be shed in vain.

Moussa is one of the expected front-runners in Egypt's upcoming presidential elections.

Israel said that members of Hamas entered Egypt near Gaza, in the Sinai desert, on Thursday then traveled south and re-entered Israeli near Eilat. Hamas has denied responsibility for the attack, but has admitted to firing rockets in retaliation for the Israeli airstrike.

We killed the head of the group that sent the terrorists, but this is just an initial response, said Israeli Prime Minister Benjamin Netanyahu. We have a policy to extract a very heavy price from those that attack us and that policy is being implemented in the field.