Tetchy relations with France were put to one side, traditional allies such as the United States, Australia and Ireland rallied behind Londoners, and the European Commission vowed to press for anti-terrorism measures across the bloc.
"This second attack unfortunately confirms that terrorism constitutes a permanent threat from which nobody is safe," the European Commission said in a statement.
"It is also vital to focus on measures which aim at preventing terrorism and particularly preventing young people from becoming radicalised."
The European Union had a strategy to fight terrorism, it said. "We need to implement this without any delay."
New York bag checks
New York ordered random bag searches on the city's train system on Thursday, as the United States voiced outrage at the second attack on the London transport network in a fortnight.
"We just live in a world where, sadly, these kinds of security measures are necessary," Mayor Michael Bloomberg said in announcing the new police searches of passengers' backpacks and packages.
Chirac expressed France's
solidarity and support to Britain
At the White House, spokesman Scott McClellan said US President George Bush has been kept closely informed about the new bomb attacks. "We are monitoring the situation closely," he said.
French President Jacques Chirac, who had swept aside Franco-British squabbles over the future of the European Union to support Blair after the deadly 7 July attacks on London, reiterated France's solidarity with Britain.
"I wish to express to the British people and to Prime Minister Tony Blair the solidarity and support of France, and I want to reiterate our determination to fight terrorism together," he said during an official visit in the Madagascan capital Antananarivo.
King Mohammed VI of Morrocco, whose country was hit by deadly urban blasts two years ago, said the latest attacks were "criminal, cowardly acts that go against the noble religious ideals of peace, tolerance, living together and the sanctity of the right to life".
Foreign Minister Abdullah Gul of Turkey, whose country has also been targeted, said "we condemn terrorism wherever it strikes and whatever its goals are".
King Mohammed VI called the
attacks cowardly and criminal
And Australian Prime Minister John Howard, who was lunching with British Prime Minister Tony Blair during an official visit to London when the news broke, said his country would stand steadfast with Britain.
"The determination of the British people to continue with their daily lives is something that we have always seen as one of the great characteristics of the people of this remarkable country," he said, standing beside Blair in Number 10 Downing Street.
"Terrorism is about the perverted use of an ideology for evil intent and for evil objectives," said Howard, a close British ally in the Iraq war.
"Canadians stand united with the British people and people around the world in denouncing all acts of violence and terrorism," said Anne McLellan, Canada's deputy prime minister and minister of public safety and emergency preparedness.
McLellan said she was "disturbed to hear of a second incident involving London's transit system, so closely following the tragic events of two weeks ago".
"Our thoughts continue to be with Londoners during this difficult time," she said.
Abdullah Gul (L) said Turkey
Other countries railed against the attackers.
Irish Foreign Minister Dermot Ahern condemned the attempt to "strike fear and terror" into the community.
Ahern said he had no doubt the British government would actively pursue those who carried out the attacks and bring them to justice.
"Those responsible should know that they will not deter the international community from combating terrorism vigorously and uncompromisingly wherever it occurs."
Spain announced it was reinforcing its border controls following the attacks, while Japan said it was putting public transportation back on alert.
Pakistan President Pervez Musharraf continued his national crackdown on fighters launched after the London bombings.
In a nationally televised speech, Musharraf also had blunt words for Britain, where all the suspected bombers of the 7 July attacks had been "born, bred and educated" and where he said Muslim fighter groups continued to operate.
Musharraf: England's problem
needs to be addressed
"We certainly have a problem here, which we are trying to address very strongly," Musharraf said. "But may I say that England also has a problem which needs to be addressed."
He named two groups, the Hizb ut-Tahrir and Al Muhajiroon, which he said were responsible for spreading a message of hate and violence.
"They had the audacity of passing an edict against my life and yet they operate with impunity," Musharraf said.