Discuss as:

London Marathon security beefed up after Boston attacks

Andy Rain / EPA

A police dog handler checks a vehicle for explosives along the Mall in London on Saturday. The Mall will stage the finish line of the London Marathon on Sunday.

LONDON – The London Marathon: 36,000 runners, 650,000 spectators, and now 40 percent more police officers. The twin blasts that killed three and wounded 176 at the Boston Marathon Monday have prompted authorities in the U.K. to boost security at Sunday’s event, with about 700 additional security officers expected along the 26.2-mile long route. 

There are already over 33,000 police in London, which is no stranger to terrorist attacks.

"There are no gaps because obviously we police this every year with the London marathon and our other agencies - British Transport Police, London Police,” the head of the Metropolitan Police's London marathon operation Julia Pendry told NBC News’ U.K. partner ITV News.

"What we have done since Boston is we've reviewed our plans, we've reviewed our contingencies and I have put on increased numbers of officers in high visibility reassurance patrols,” she added.

The increase was meant to “make sure that when people step into the capital on Sunday they feel hopefully reassured and safe,” she said.

Police in London are boosting security at Sunday's London Marathon after the attacks in Boston.

While U.K. officials have years of experience coping with security challenges – London has spent decades under the threat of bombs, first from Irish Republicans and more recently jihadists –a marathon is by its nature a potential security headache.

The race route is set to take runners past important and iconic sites – including Tower Bridge, the Houses of Parliament and Buckingham Palace – as well as through Canary Wharf, the riverside financial district targeted by the Irish militants in the 1990s. 

In a statement released on Saturday, London Marathon chief executive Nick Bitel also acknowledged “additional security issues ahead of Boston, but that seems be bedding down and the message of reassurance to runners very well received.”

Related: Runners, fans determined not to shy away from London Marathon

Related: London beefs up marathon security

Marathon organizers and security officials would not go into great detail about security preparations, but they would likely have been watching the dramatic events unfold in Boston.

Jared Wickerham / Getty Images

Cheers filled the streets after a Boston Marathon bombing suspect was captured alive but wounded Friday night — following a daylong manhunt that shut down the city.

On Friday night, Boston police captured bombing suspect Dzhokhar Tsarnaev, 19. The arrest capped a manhunt that had the city of Boston and its suburbs locked down after the execution of a college campus patrol officer, a carjacking and the death of Tsarnaev's 26-year-old brother, Tamerlan, during a 200-bullet confrontation with cops.

British officials were keen to point out that there had been no change to the threat level and nothing to link the London marathon to the two bombings in Boston.

“There is no change in the threat in London,” Pendry said.

Despite any preparations, it would be impossible to make the marathon completely immune to attack, according to security expert Margaret Gilmore.

“You can’t ever guarantee safety,” said Gilmore, a senior research fellow specializing in homeland security at Royal United Services Institute, the U.K.'s top defense and security think tank.

Organizers were also planning to commemorate those killed and injured in Boston by holding a 30-second silence before each of the race’s three starts and handing out black ribbons to every runner. They also announced that they would donate around $3 to the Boston First fund for every finisher.

The Associated Press contributed to this report.

Related:

What's next: The interrogation of the Boston bombing suspect

How thermal imaging helped catch bomb suspect

Timeline of terror hunt, from first photos to final fight