The bombings coincided with President George W. Bush's visit to London. They were quickly blamed on al Qaeda, were the worst terrorist bombing in the Muslim nation's history.
At least 450 people were also injured, said Interior Minister Abdulkadir Aksu.
The explosions, just minutes apart, came just days after suicide bombers struck two Istanbul synagogues, killing 23. That attack was also blamed on al Qaeda.
British Consul-General Roger Short and a second British diplomatic staff member Lisa Hallworth were among the dead. British Foreign Minister Jack Straw rushed to Istanbul.
"Once again we are reminded of the evil these terrorists pose to people everywhere and to our way of life," Prime Minister Tony Blair said in London. "There must be no holding back, no compromise, no hesitation in confronting this menace."
An unidentified caller to the semiofficial Anatolia news agency said al Qaeda and a small military Turkish group, the Islamic Great Eastern Raiders' Front, or IBDA-C, jointly claimed responsibility for attacks.
Witnesses said one pickup truck exploded in front of the HSBC bank building devastating its 18-story facade. The second crashed through the gate of the British consulate destroying annexes to the main building.
The vehicle that hit the British consulate looked like a food delivery truck with the explosives in large metal food containers, Anatolia quoted police as saying.
"Cars were flying, there was blood everywhere," said Mehmet Dag, 26, a delivery man who was just 100 meters (yards) away from the consulate building when the blast took place.
Turkish Premier Recep Tayyip Erdogan vowed to defeat the attackers, who struck during the Islamic month of Ramadan.
"Those who bloodied this holy day and massacred innocent people will account for it in both worlds," he said. "They will be damned until eternity."
In a telephone conversation with Blair, Erdogan vowed to step up his nation's fight against terror.
"There is no faltering," Erdogan said, according to Anatolia. "We shall continue our fight against terrorism with more fervor."
Aksu said the attacks were carried out by suicide bombers and were similar to the synagogue bombings, in which hundreds of pounds (kilograms) of fertilizer-based explosives were packed into trucks.
Aksu said that at the British consulate the "man came, rammed into the gates with a speeding truck, set it off, blowing himself up."
A second bomb exploded moments later in from of the HSBC bank's headquarters in the affluent Levent district of Istanbul. HSBC is the world's second largest bank.
The explosion was so strong that it scattered body parts and bloodied pieces of charred metal across the four-line highway in front of the building and into a cemetery on the other side of the road.
A policeman could be seen in the cemetery collecting body parts, including a charred, severed leg that he put inside of a plastic bag.
Burned out cars, some with their doors blown open, sat in front of the building. The smoke and stench of burning wires was so strong that some police at the site wore surgical masks.
The blast sheared off the white facade of the building, exposing the gray cement beneath.
The windows of the building were blown out and scraps of white ceiling material dangled down, caught on torn electrical wires swaying in a soft breeze.
The second bomb tore apart the wall surrounding the garden of the British consulate in Beyoglu, a historical district that is popular with tourists.
The U.S. consulate moved months ago from Beyoglu to a remote area outside of central Istanbul.
Injured covered in dust from the debris and blood staggered away from the area. Two women stood outside of the consulate crying and shouting for their relatives.
Shattered glass littered the area.
Almost 100 Turkish troops were deployed after the blast. At least a dozen of the soldiers, wearing helmets and camouflage uniforms and armed with G-3 assault rifles, stood by their jeeps near the HSBC headquarters. The troops later were withdrawn to their barracks.
Such a deployment is sensitive in Turkey, where the military took power three times between 1960-80. The last coup came after years of street clashes between left wing and right-wing fighters left some 5,000 dead. The coup came at the height of the violence when some 20 people were being killed every day.
U.S. President George W. Bush, who met with Blair Thursday, said the bombing showed "utter contempt for innocent life."
"The terrorists hope to intimidate, they hope to demoralize. They are not going to succeed," Bush said at a news conference with Blair.
In Washington, U.S. Attorney General John Ashcroft said the attacks bore the marks of an al Qaeda operation.
"They appear to be in the method of operation, or in the operational style, of al Qaeda or al Qaeda operatives or affiliates," he said.
It was the highest single-day death toll from terrorism in Turkey since 1977, when gunmen opened fire on leftists celebrating May Day, killing 37.
Turkey's stock market started falling immediately after the attacks and was closed minutes later after plummeting 7 percent and will remain closed Friday. The central bank said it would take steps to prevent any fallout from the attack.
Turkey has been recovering from its worst recession in decades and there were fears that the continuing attacks could harm the lucrative tourism sector and scare away foreign investors.
Several countries including Britain warned citizens to stay away from Turkey, prompting a complaint from Erdogan. Europe's soccer authorities postponed international games in the country.
The nearby U.S. consulate was moved months ago to a new, more secure location in another district.
State Department officials say they know of no Americans among the injured in the bomb blasts.
However, the U.S. consul general there has issued an advisory to Americans to stay away from the area, says CBS News Reporter Charles Wolfson. Diplomatic staff in Istanbul and at the U.S. Embassy in Ankara are evaluating their own security precautions, officials say.
Authorities arrested six people Wednesday in connection with the synagogue bombings. A court charged five with "attempting to overthrow the constitutional structure," which carries a sentence of life imprisonment. The sixth was charged with "helping illegal organizations," punishable by five years in prison, Anatolia said. No trial date was set.
The two suicide bombers who attacked the synagogues were identified as Turks who according to Foreign Minister Abdullah Gul had visited Afghanistan. Turkish authorities were investigating links with al Qaeda.
Al Qaeda and the Turkish IBDA-C also claimed responsibility for that blast.