GAZA CITY- Israeli air raids on Gaza killed five Hamas militants on Saturday as the Jewish state warned the United Nations it will defend itself against Palestinian rocket attacks from the isolated territory. Egypt meanwhile opened its border with the besieged coastal strip to allow dozens of sick and wounded Gazans to enter for medical treatment. The first overnight raid, which killed two Hamas militants near Rafah at the southern end of the strip, was aimed at a police station used by Hamas, the head of Gaza emergency services, Dr. Muawiya Hassanein, said. The second attack targeted another Hamas police base in the city of Khan Yunis in the south of the territory and killed three members of the Hamas-run paramilitary group that polices the territory, he said. The third strike took place east of Khan Yunis, wounding two Palestinian militants from the Islamic Jihad movement, medics said. An Israeli army spokeswoman confirmed the raids, saying "there were two aerial attacks against Hamas posts and and one against gunmen approaching the (border) fence in the south." Palestinian militants meanwhile fired more than a dozen rockets at Israel, with three striking the hard-hit town of Sderot. One of the rockets hit a house, but no one was wounded in the attacks. Israeli troops and Palestinian militants have clashed on a near-daily basis since Hamas seized power in June last year as Israel's political and military leaders have mulled a larger offensive in the impoverished territory. In a letter sent to UN Secretary-General Ban Ki-moon on Saturday, Israel warned that it "will not remain idle while our citizens are constantly targeted by terrorist attacks. Israel will know how to defend itself." A 48-year old Israeli man was killed on Friday by a mortar round fired from the Gaza Strip, the first person to be killed by a mortar round since Israel withdrew troops and settlers from Gaza in 2005, the army said. Rocket attacks have meanwhile claimed the lives of 14 people since 2000. The military wing of Hamas said it carried out Friday's attack on Israel. Since Israel and the Palestinians relaunched formal peace talks in November at least 458 people have been killed, most of them Gaza militants, according to an AFP count. On Saturday, Egypt opened the Rafah border crossing for the first time in months to allow hundreds of Gazans to leave for medical treatment. "We will transport 550 patients in 40 Palestinian ambulances and five trucks," Hassanein said, adding that the patients include 200 people wounded in Israeli military operations and 70 children under the age of 16. Scores of weary Gazans gathered outside the terminal as black-clad Hamas gunmen paced through the crowds and kept onlookers away from the crossing. "We hope Rafah will stay open like before. The health situation in Gaza is very serious. There is no medicine, nothing," said Mufid Habush, as he waited at the crossing with his five-year-old daughter. The little girl, whose leg was amputated because of a birth defect, was due to have an operation in Egypt. By Saturday afternoon Egyptian forces had allowed only a few dozen patients to cross, an AFP correspondent at the border reported. Hamas said the crossing would be open for three days to allow the sick to enter for treatment and those trapped on one side or the other to cross back to their place of residence. "We hope this will be the first step towards permanently opening the crossing and breaking the siege," senior Hamas official Ismail Radwan told AFP. Since Hamas seized power Israel has sealed the territory of 1.5 million people off to all very limited humanitarian aid in a bid to put pressure on Hamas to halt rocket attacks. Israel has been threatening a wider ground offensive for months, one that would seek to topple the Hamas government as well as try to put an end to militant rocket and mortar fire. But the Jewish state was expected to hold off until after its 60th anniversary celebrations, most of which took place on Thursday, and a visit by US President George W. Bush next week.