Colonel Timothy Alben, superintendent of the Massachusetts State Police, speaks to the media in Framingham regarding security measures for the upcoming Boston Marathon on April 21. Picture: Elise Amendola

New York -

Spectators will pass through rigorous security screening at this year's Boston Marathon and they are encouraged to bring only small items in clear plastic bags in order to get through the screening faster, according to new security measures introduced on Monday.

The restrictions were announced as the city prepared for the first marathon since a terrorist bomb attack last year killed three people and wounded more than 250.

“In this world, you never eliminate risk,” said Massachusetts State Police Colonel Timothy Alben as the measures were announced, the Boston Globe reported.

“You never bring it down to zero. But we are working very hard at reducing the risk.”

This year's marathon is scheduled to be held on April 21.

In addition to carrying personal items in clear plastic bags, spectators are encouraged to avoid bringing backpacks, coolers and containers capable of carrying more than a litre of liquid. Police presence will be doubled to 3 500 officers patrolling the route of the marathon.

Runners will not be allowed to carry any backpacks, large containers or bulky items inside any marathon venue, and they also won't be allowed to wear costumes that cover their faces or that are not form-fitting.

Security measures during the marathon will be provided as a collaboration among local, state and federal law enforcement, said US Secretary of Homeland Security Jeh Johnson, who met with Boston Mayor Martin Walsh on Monday to discuss plans for the event.

The organisers of the marathon will hold a memorial event on April 15 to honour the victims of last year's bombing.

In January, prosecutors said that the United States would pursue the death penalty against Boston bombing suspect Dzhokhar Tsarnaev, 20, who pleaded not guilty to charges that he carried out the bombings along with his brother at the finish line of the Boston Marathon.

Tsarnaev's older brother, Tamerlan Tsarnaev, was killed during the police chase a few days afterward. After being wounded by police, Tamerlan Tsarnaev was run over by the car Dzhokhar used to flee the shootout. Dzhokhar was discovered later hiding inside a small boat dry-docked behind a house.

Authorities say he left a confession in which he justified the bombings as vengeance for US military action in Muslim countries. - Sapa-dpa