A bomb exploded on a bus in Tel Aviv as it passed by Israeli army headquarters around noon Wednesday.
The attack, which police said left 18 passengers injured, shook up the Israeli public and threatened to complicate efforts to achieve a cease-fire on the eighth day of violence between Israel and Gaza.
The bus attack left three people hospitalized in serious condition, police spokesman Mickey Rosenfeld said. Another 15 were treated for minor injuries, he said.
Hamas praised the attack but did not claim responsibility.
"We told you #IDF that our blessed hands will reach your leaders and soldiers wherever they are," the al Qassam Brigades, the military wing of Hamas, said on Twitter. "You opened the Gates of Hell on Yourselves."
Meanwhile, overnight and into Wednesday, Israeli bombs and artillery turned buildings, tunnels and bridges in Gaza into rubble in 100 strikes confirmed by Israeli authorities. At the same time, Hamas media boasted about their militants' rockets hissing off in the direction of populated areas of southern Israel.
U.S. Secretary of State Hillary Clinton shuttled from meetings with Palestinians to Israeli leadership Wednesday, after hopes of an imminent agreement between Hamas and Israeli leaders that could have halted the explosive carnage at least for a while dissolved Tuesday.
Clinton met early with Palestinian Authority President Mahmoud Abbas in Ramallah in the West Bank, according to the U.S. Embassy, and will sit down with Israeli Prime Minister Benjamin Netanyahu in Jerusalem for a second day.
U.N. Secretary-General Ban Ki-moon also met with Abbas in Ramallah Wednesday morning.
"Today the situation in Gaza is deeply alarming," Ban said, standing next to Abbas at a new conference.
"Rockets aimed at military targets inside Gaza are killing and injuring civilians and damaging... civilian infrastructures."
Ban sadly recalled his visit in 2009 during the Israeli incursion into Gaza, Operation Cast Lead.
"It is quite painful for me as secretary-general and also personal(ly) as a human being to be back for the same reason," he said.
He demanded that diplomacy pave the way forward and called for the emergence of a Palestinian state.
Clinton is also to meet with Egyptian President Mohamed Morsy, who is working to broker a cease-fire.
Clinton is not expected to travel to Gaza, which is run by Hamas, considered a terrorist organization by the United States and other countries.
Pope Benedict, speaking from Vatican City, called Wednesday for both sides to end the violence.
"I feel the duty to reiterate once again that hatred and violence are not the solution to problems," he said.
Israeli television showed images of white smoke rising up from the bombed public transportation bus in Tel Aviv, but from the outside the vehicle appeared intact. At least one passenger was taken out on a stretcher.
An unexploded bomb was still on the bus, said Ofir Gendelman, spokesman for the Israeli prime minister.
At the scene of the bus bombing, police cordoned off the street as ambulances arrived.
There is a hospital nearby, said CNN's Sara Sidner. An eyewitness told her that the windows of the bus were shattered and a bomb squad has approached it.
Rumors of a suicide bombing circulated on social media and Hamas' TV station, but accounts by authorities and witnesses seemed to quickly dispel them.
"A bus explodes under my Tel Aviv office," said military spokeswoman Avital Leibovich on Twitter. "Possibly due to a bomb or suicide bomber. Hearing the sirens of the ambulances."
No one was found dead on the bus, according to authorities. Two people, speaking live on Israeli radio, said they witnessed the attack and that they saw a male throw a bag into the bus and then run away after the explosion.
Israel's Channel 10 reported that one suspect had been apprehended.
Hamas put its own spin on the attack in a banner on al-Aqsa.
"Hamas blesses the suicide bombing and assures that it is a natural response to the massacre of the al-Dalou family and targeting of innocent Palestinian civilians."
A rocket alarm howled over Ashkelon on the Israeli side shortly after 7:30 a.m. Wednesday, just minutes after Hamas' TV broadcaster al-Aqsa reported its militants' rockets striking there as well as in the towns of Sderot and Ashdod.
Since midnight, 17 rockets out of Gaza have touched down in Israel, the IDF confirmed. The Iron Dome protection system intercepted 12 more.
CNN's Fred Pleitgen in Ashkelon heard two impacts but could not yet say if the rockets hit anything or were eliminated mid-air by the rocket defense system.
The Israel Defense Forces overnight targeted "dozens of terror infrastructure sites," including the Ministry of Internal Security, which it saw as Hamas' "main command and control center." It took aim at a police compound, a "military hideout," and other targets linked to what it called Hamas' "terror activity."
The Israeli military also struck a media building, where it said Hamas "deliberately located" an "intelligence operation center," and a system of tunnels used to transport fuel.
Al-Aqsa said two of their journalists were killed when an Israeli strike targeted their car. The IDF confirmed the strike but said the two killed were Hamas operatives. Residents participated in a public funeral for the two.
The IDF also confirmed targeting bridges in central Gaza.
Gazan authorities have reported at least 139 people killed in the conflict as of Wednesday. Israel reported a total of five Israelis killed as of Tuesday.
According to the Gaza Ministry of Health, 27 people were killed Tuesday, including children. More than 1,100 people have been injured. It's not clear how many of the victims were militants.
More than 70 people have been injured in Israel, including soldiers, Israeli officials have said.