The suicide bombings on London's transport system on July 7 of 2005 killed 52 people
"It will take 20 to 30 years to defeat the scourge of terrorism with vigilant effort," King Abdullah said.
"And I strongly urge all countries in the world, including Great Britain, to take the matter of fighting terrorism very, very seriously."
A spokesman for Gordon Brown, Britain's prime minister, said no warnings were received before the attacks: "We made it very clear at the time that no specific warnings were received from any source."
"We do have a very close intelligence relationship with the Saudis," he said.
"We just happen to disagree on this point."
King Abdullah was due to arrive in Britain on Monday for a state visit. He is the first Saudi monarch to visit Britain in 20 years.
His visit has prompted protests from critics of the Saudi Arabia's human rights record.
"The UK should question Saudi Arabia about its domestic and religious culture and the source and root of terrorism in Saudi Arabia and how it is exported abroad," Mai Yamani, a Saudi political analyst, told Al Jazeera.
Demonstrations are planned outside the Saudi embassy in London later this week.