Even on eve of a nuclear security summit, most people in Washington might not feel any remarkable difference between this weekend and any others.

Police cars park outside the Washington Convention Center in Washington D.C., capital of the United States, April 11, 2010. Washington beefed up its security for the upcoming Nuclear Security Summit due on April 12 and 13. [Zhang Jun/Xinhua]

Residents were enjoying sunshine and breeze before the Washington Monument, and were attracted by cherry blossoms alongside the Tidal Basin.

However, the U.S. capital has received an "immense level" of security service and is well prepared for the summit, which is believed to be the largest gathering of world leaders in the city in more than 60 years.

During the two-day summit hosted by President Barack Obama, leaders from 47 nations will discuss ways of securing nuclear materials from terrorists -- "the most immediate and extreme threat to global security" as identified by Obama.

The summit is "without any question one of the biggest, most prestigious important meetings that has ever taken place not just in this city but anywhere in the world," according to Washington Mayor Adrian Fenty.

Security service has been beefed up inside and around the Washington Convention Center where the summit is to be held and the hotels where the world leaders are to stay.

The convention center was closed at 5 p.m. and roads around it will shut down around 10 p.m. on Sunday for a comprehensive security clean-up.

Some major streets nearby have been separated with 10-foot-tall iron fences, while buses and subway trains have been ordered to skip the Mt. Vernon Station, which is close to the center, on Monday and Tuesday.

Reports here said that during the summit, residents will have to show ID to get into their homes inside the cordon, and non-residents won't be allowed inside the cordon.

Major security agencies, including Federal Bureau of Investigation, Secret Service, Diplomatic Security Service and Coast Guard, will reportedly conduct "their operations in real-time using encrypted digital radios on existing frequencies."

During the G8 summit in L'Aquila, Italy, last July, President Obama urged the international community to work together to collectively improve the nuclear security culture, share the best practices and raise the standards for nuclear security.

The upcoming summit will focus on the security of nuclear materials, leaving other broad topics such as nonproliferation, disarmament and peaceful nuclear energy to different forums, said the White House in a statement.

Leaders of Iran, Syria, and the Democratic People's Republic of Korea will not attend the summit. Israeli Prime Minister Benjamin Netanyahu has decided to cancel his scheduled trip to Washington.

Presidents of China and Russia, Prime Ministers of India and Pakistan reportedly are expected to receive a level of security protection only lower than that to President Obama, but higher than that provided to Vice President Joe Biden.