Palestinian medics say that more than 280 people have been killed and more than 600 injured as Israel's bombing of the impoverished Gaza Strip continued for a second day.
A police station and a factory were among the sites reportedly hit on Sunday, after a mosque and the headquarters of al-Aqsa television had been struck overnight.
Reports said air attacks on Sunday afternoon struck east of Gaza City, in Khan Yunis, and Jabaliya, in the north.
Witnesses also reported seeing more than 10 explosions along the border with Egypt close to sunset, in what was said to be an attack on underground tunnels used to smuggle goods into Gaza.
Many people were said to be reported wounded in the strike.
The Reuters news agency said that at least one missile hit the offices of Ismail Haniya, the Hamas leader in the Gaza Strip, but he was not in the building at the time.
Ehud Barak, Israel's defence minister, warned that the air raids could be followed by a major ground incursion into the Gaza Strip.
"We are ready for anything. If it's necessary to deploy ground forces to defend our citizens, we will do so," Barak's spokesman quoted him as saying on Sunday.
Israeli television has reported that hundreds of infantry and armoured forces were massing on the border of the territory, and on Sunday the army was given approval to call up reservists to bolster its fighting strength.
Ayman Mohyeldin, Al Jazeera's correspondent in Gaza, said: "There are two strands of suffering - ordinary Palestinians who are not targeted in these attacks, and those that are.
"It is a very grim picture for ordinary civilians. They are suffering from fuel outages and a shortage of supplies.
"About 750,000 people who depend on food distribution by aid agencies have not been able to receive supplies because the agencies cannot operate due to the siege.
"For those immediately affected by the more than 24-hour bombardment, the picture is even more grim. They need special medical attention and supplies that the hospitals, doctors and medical officials say they simply don't have."
The United Nations Security Council urged an immediate halt to all military activities in the Gaza Strip and called for the humanitarian crisis faced by Gaza's 1.5 million residents to be addressed.
|Gaza's population is already suffering chronic shortages of basic supplies [AFP]
Neven Jurica, Croatia's ambassador to the UN and president of the council, read out a non-binding statement on behalf of the 15-member body that called on the parties involved in the conflict "to stop immediately all military activities". The statement, however, did not mention either Israel or Hamas by name.
More than 230 targets have been hit with missiles fired from helicopter gunships and fighter jets since Israel launched Operation Cast Lead on Saturday, an Israeli military spokeswoman said.
"They include Hamas infrastructure like buildings, arms depots and rocket-launching zones," she said.
On Sunday, Israeli police said a Palestinian missile had hit near the town of Ashdod, more than 30km from the Gaza Strip. The attack would be the furthest inside Israel yet.
Al Jazeera's Jacky Rowland, reporting from Jerusalem, said that Israeli authorities were anticipating an increase in Palestinian rocket attacks.
"The home-front defence has drawn up action plans for people living within 30km of the Gaza Strip, people living in those areas have strict instructions to stay within range of a bomb shelter and not to gather outdoors in large groups," she said.
"Some defence officials are anticipating that up to 200 rockets a day could be fired from Gaza."
At least one Israeli was killed and six others wounded in retaliatory missile attacks by Palestinian fighters on Saturday.
Mustafa Barghouthi, a member of the Palestinian Legislative Council, rejected the Israeli government's claims that the air raids were in self-defence.
"This is a bloodbath, the bloodiest bloodbath since 1967," he told Al Jazeera. "This is an attack on the civilian population of Gaza."
|Israeli troops have reportedly been massing on the border of the Gaza Strip [AFP]
"They try to claim that this was done as a response to missiles, but they are denying the fact that the whole year not a single Israeli was killed by missiles. The first Israeli killed was only because of the Israeli invasion, the Israeli attack."
Many of the dead in Saturday's attacks were police officers, including Tawfiq Jabber, the Gaza chief of police.
Ofir Gendelman, a spokesman for the Israeli foreign ministry, suggested that casualty figures put forward by the Palestinians were misleading and insisted that only Hamas targets had been hit.
"Hamas is using figures to attract public attention, media attention and for propaganda purposes," he told Al Jazeera.
"At the end of the day we are attacking Hamas strongholds ... No civilian targets are hit, it is very unfortunate that some civilians will be hit."
Mahmoud Abbas, the Palestinian president and leader of the rival Fatah group, blamed Hamas for the violence.
"We talked to them [Hamas] and we told them 'please, we ask you, do not end the truce. Let the truce continue and not stop' so that we could have avoided what happened," he said after talks with his Egyptian counterpart on Sunday.
A six-month truce between Israel and Hamas in the Gaza Strip ended on December 19.
Hospitals, already suffering from shortages due to an 18-month blockade on the Gaza Strip, said they were struggling to cope with the number of injured, which includes women and children.
One of the buildings hit on Sunday was reportedly a warehouse used to supply local pharmacies with medicines.
"This is going to make us unable to supply any of the local families that depend on us," Dr Hussam Abu Hashem, the owner, told local Hamas radio. "It's a war against human beings."