An explosion ripped through a bus in central Tel Aviv around noon on Wednesday — the first bombing attack in the city since 2006.

Twenty-one people were injured in the bombing, three of them seriously. No one was killed.

Police commander Yohanan Danino said police had been “braced for an attack of this kind.”

There was an ongoing threat of more attacks, he said: “We’re not only facing rocket attacks, that’s clear,” he said. “People need to be alert, to report anything suspicious.”

The United Nations, the US, and several European countries condemned the attack.

A Hamas spokesman praised the bombing, but stopped short of taking responsibility, Reuters reported. Israeli authorities did not immediately ascribe responsibility to a Palestinian group.

“Hamas blesses the attack in Tel Aviv and sees it as a natural response to the Israeli massacres,” spokesman Sami Abu Zuhri told Reuters.

“Palestinian factions will resort to all means in order to protect our Palestinian civilians in the absence of a world effort to stop the Israeli aggression,” he said.

Sweet cakes were handed out in celebration at Gaza’s main hospital in response to news of the bombing, Reuters reported. According to other reports from Gaza, celebratory gunfire was audible as the bombing was reported on the radio.

The of the bus bombing in Tel Aviv, on Wednesday, November 21 2012 (photo credit: screen capture/Channel 10)

The scene of the bus bombing in Tel Aviv, Wednesday, November 21, 2012 (photo credit: screen capture/Channel 10)

The explosion on the Dan bus took place on the corner of two major Tel Aviv thoroughfares, Shaul Hamelech and Weizmann, in an area with many office buildings and heavy pedestrian traffic. The Kirya compound, headquarters of the Israeli military, is nearby.

According to reports, a man was seen placing a bag on the bus and then running away, leading to a police chase through the streets of Tel Aviv. There were also unconfirmed reports of a second suspect. Police arrested at least one person in connection with the bombing, in the stock market compound in nearby Ramat Gan.

Police arrest a suspect in the Tel Aviv bus bombing, Wednesday (photo credit: Channel 2 screen capture)

Police arrest a suspect in the Tel Aviv bus bombing, Wednesday (photo credit: Channel 2 screen capture)

“It’s a big, huge mess,” an eyewitness told Channel 10. “There was a very big boom and a lot of ambulances. It wasn’t clear what happened.”

Police, security forces, ambulances and a crowd of onlookers converged on the scene shortly after the explosion.

The scene of the bus bombing in Tel Aviv, Wednesday (photo credit: Channel 2 screen capture)

The scene of the bus bombing in Tel Aviv, Wednesday (photo credit: Channel 2 screen capture)

The last Palestinian bombing in Tel Aviv, Israel’s financial and cultural capital, took place in April 2006. In that attack, an Islamic Jihad suicide bomber detonated himself at a shwarma restaurant, killing 11 and wounding dozens.

The last suicide bombing in Israel was in February 2008, in the southern town of Dimona. One Israeli was killed.

In recent years, there have been scattered stabbing attacks and attacks using motor vehicles, but bombings in Israel’s cities had all but ceased before Wednesday.

UN Secretary-General Ban Ki-moon condemned the attack.

“The Secretary-General was shocked at the news of the terror attack on a bus today in the center of Tel Aviv. He condemns this attack in the strongest possible terms,” read a statement from his office.

“There are no circumstances that justify the targeting of civilians. The Secretary-General is saddened and expresses his sympathy to those injured in the blast.”

In Jerusalem, US Secretary of State Hillary Clinton said the US administration “strongly condemns” the bombing.

“The United States stands ready to provide any assistance that Israel requires,” she said.

Condemnations also arrived from Britain, France, Germany and elsewhere.