ISTANBUL, Turkey (CNN) -- The British consul general was among at least 26 people killed when explosions rocked Istanbul, Turkey's largest city.

Diplomatic sources told CNN that Consul General Roger Short was killed after a car bomb exploded on a narrow street outside Britain's Istanbul consulate, one of at least two explosions in the city Thursday.

Father Ian Sherwood of the Anglican Church in Istanbul told CNN: "I've been with the family of consul general since it happened and, sadly, the consul general is dead."

Another blast destroyed part of the London-based HSBC bank headquarters near a shopping mall. As many as 450 people were injured in the explosions, Turkish officials said.

Thursday's blasts come just days after two suicide bombers attacked synagogues in Istanbul, killing 23 people and the bombers.

British Foreign Secretary Jack Straw said Thursday he had information there were as many as five coordinated explosions, which he described as "a clearly appalling act of terrorism."

"At this stage we can't say who is responsible," Straw told reporters in London, but he added the blasts bore "all the hallmarks" of the international terrorism of al Qaeda and associated groups.

British Prime Minister Tony Blair and U.S. President George W. Bush, who is on a state visit to the UK, condemned the Istanbul blasts and vowed they would not be deflected from the war against terrorism or trying to rebuild Iraq.

Speaking at a joint news conference with Bush, the prime minister said the attacks in Turkey showed how important it was for coalition forces to "carry on" their mission in places like Iraq.

"We stay until the job gets done," declared Blair. (Bush, Blair: Defeat this menace)

Shortly after Thursday's explosions, a government office in Istanbul received a phone call from al Qaeda and a Turkish Islamic militant group -- the Great Eastern Islamic Raiders' Front (IBDA-C) -- claiming joint responsibility for the attack, CNN Turk reported.

IBDA-C initially claimed responsibility for twin attacks Saturday.

Turkish officials have confirmed two explosions -- one in the Levent neighborhood outside the HSBC headquarters, near a shopping mall, and the other in the Taksim area, outside the British consulate, both crowded areas in Istanbul.

The Britain Foreign Office has advised against non-essential travel to Turkey as a result of the bomb blasts. (UK issues Turkey travel warning)

Eyewitnesses said they believe the blasts were caused by suicide car bombers.

Turkish Interior Minister Abdulkadir Aksu warned against speculation on which group is responsible for the attacks, saying that could hamper the investigation.

"We are still considering all the options," Aksu said, speaking to the media shortly after landing in Istanbul from Ankara. "Our state security court and public prosecution (have) brought in a ban on the coverage and this has been done to investigate the incident more properly." (Turkey: We will not bow to terror)

The explosion outside HSBC headquarters in Levent happened shortly before 11 a.m. (4 a.m. ET). Video of the HSBC building showed extensive damage to the exterior.

A CNN Turk reporter on the scene said there was a large hole outside the bank headquarters, possibly where the explosion originated.

Video of a shopping mall near the HSBC bank showed chaos with people streaming out of the area, some with bloody faces and blood-soaked clothes. Shattered glass and burned vehicles littered the street. (Chaos and panic in Istanbul)

HSBC spokesman in London, Adrian Russell, said two of the bank's buildings were hit Thursday.

"With reference to the shocking events in Istanbul this morning, unfortunately two HSBC buildings have been struck by the bomb blasts across the city, including our head office in Levent, " Russell said. "It is with deep regret that we have to confirm that there have been a number of fatalities."

Chris Kitrinos, an English teacher at a school adjacent to the British consulate, said the damage there was "very extensive." The school's windows had been blown out and police told CNN Turk that the consulate's outer wall had been destroyed.

"I walked by the consulate every day and I've been concerned because traffic has continued to drive by," Kitrinos said. "I was worried about the proximity (to the consulate), I was afraid for myself and now, of course it's happened."

The British consulate was targeted in April when an explosive device was hurled at the building, the UK's Press Association reported. No one was injured in that incident.

The Istanbul stock exchange was closed following the blasts, Reuters reported.

Meanwhile, Istanbul's governor has confirmed the identities of two Turkish men that authorities believe committed Saturday's twin suicide attacks on the synagogues. (Full story)

Mesut Cabuk, 29, attacked the Beit Israel synagogue, and Gokhan Elaltuntas, 22, attacked Neve Shalom, Gov. Muammer Guler told a news conference Wednesday. DNA testing confirmed their identities.