French PM Dominque de Villepin added: "More than ever, democracies must rally together and show unity in the face of the terrorist threat. More than ever, we must show vigilance and determination."

French members of parliament suspended work in solidarity with the victims.

The Queen said she was "deeply shocked" by the explosions.

US President George W Bush, at the G8 summit in Gleneages, said he was "impressed" with the resolve of all the leaders to fight terrorism.

Pope Benedict XVI condemned the attacks as "inhuman and anti-Christian," in a telegram to the Archbishop of Westminster, Cardinal Cormac Murphy O'Connor.

He added he learned of the attacks "with pain" and wanted to assure the victims and their families that he was spiritually close to them.

The Spanish government issued a statement strongly condemning the "savage attacks" that rocked London and expressed its solidarity with the British people.

The US had no plans to up their own state of terror alert, the White House said.

But officials in Washington confirmed bomb-sniffing dogs and armed police officers were now patrolling the city's subways and buses.

Candace Smith, spokeswoman for the Washington Metropolitan Area Transit Authority, said security in the city's transit systems was stepped up "immediately".

The Australian Foreign Affairs office immediately set up a helpline for families who have relatives in the UK while Israeli ambassador to London, Zvi Hefetz, said that the embassy was in a state of emergency following the explosions.