Tory leader David Cameron has pledged to "work as closely as I can" with the government to make the country safe, after a car bomb was found in London.
David Cameron praised the public and police
He said the discovery was "a reminder of the huge threat that we face as a country from terrorism".
Police defused the bomb and removed the car from Haymarket in central London while the streets remain sealed off.
PM Gordon Brown said the public must remain alert as the country faces "a serious and continued threat".
A controlled explosion was carried out on the car, packed with 60 litres of petrol, gas cylinders and nails, in the early hours on Haymarket, near Tiger Tiger nightclub.
As police continued to search the area, Mr Cameron said: "It is a reminder of the need to be incredibly vigilant, it's a reminder of the huge threat that we face as a country from terrorism.
"I think we should praise the public, who have been vigilant, we should praise the police and the security services for the work that they do, and we must remain at the highest state of alert."
He added: "I will work as closely as I can with the government to make sure we do everything to make our country as safe as possible."
He said he was in touch with government through his office and hoped to meet Mr Brown in the future.
Both the prime minister and Home Secretary Jacqui Smith have urged vigilance.