Helicopters will patrol the temporary no-fly zone around New Jersey's MetLife Stadium Sunday, with F-16s based in Atlantic City ready to be scrambled if an unauthorized aircraft does enter the restricted airspace.

Down below, bomb-sniffing dogs will patrol the trains and buses that are expected to take approximately 30,000 of the 80,000-plus spectators to Sunday's Super Bowl between the Denver Broncos and Seattle Seahawks.

The Transportation Security Administration said it has added about two dozen dogs to monitor passengers coming in and out of the airport around the Super Bowl.

On Saturday, TSA agents demonstrated how the dogs can sniff out many different types of explosives. Once they do, they're trained to sit rather than attack, so as not to raise suspicion or create a panic.

TSA spokeswoman Lisa Farbstein said the dogs undergo 12 weeks of training, which costs about $200,000, factoring in food, vehicles and salaries for trainers.

Dogs have been used in cargo areas for some time, but have just been introduced recently in passenger areas at Newark and JFK airports. JFK has one dog and Newark has a handful, Farbstein said.

The TSA has also added 200 screeners at Newark to handle the larger volume of travelers, and Farbstein said TSA agents from LaGuardia Airport will be performing screening on train passengers at New York Penn Station and New Jersey's Secaucus Junction on Super Bowl Sunday.

Despite no specific terror threats against the game, officials say suicide attacks on a trolleybus and a train station in Russia that killed more than 30 people within weeks of the Winter Olympics have raised worries among authorities, Reuters reported.

"Of particular concern to us is what was going on overseas in Volgograd in regard to the Sochi Olympics. As you know both of those bombings were targeting mass transit," Col. Rick Fuentes, head of the New Jersey State Police, told reporters this week. "That is a concern with the mass transit; we've prepared ourselves for it."

The Transportation Security Administration said Friday that all fans boarding trains to the stadium from Secaucus Junction Station, the start of NJ Transit's 6.8-mile line to the stadium in East Rutherford, must pass through a security checkpoint manned by TSA agents.

Only people who show agents a valid Super Bowl ticket will be allowed to pass through the security checkpoint and board a train, said John Durkin, special agent in charge of the TSA Newark field office.

Fans will only be allowed to carry a small clutch bag or purse that's no bigger than 6.5 by 4.5 inches and a clear plastic bag that's about as big as a freezer storage bag, per the NFL's bag policy. TSA will not have a place to store larger bags, and a person will not be allowed to clear security and get on the train with one.

The checkpoints started Friday and will be random until Sunday, when they turn mandatory for all people taking the train to MetLife Stadium. Friday agents were swabbing women's' bags to check for explosives.

Fans will also have to go through metal detectors and regular security at the stadium as well.

Officials estimate between 12,000 and 15,000 passengers will ride the train between the Secaucus station and the stadium. Ten double-decker trains capable of carrying up to 1,350 passengers each will run to the stadium.

Durkin said agents will be looking "for anything that could negatively affect the safety of New Jersey Transit passengers."

Meanwhile, the Defense Department said Friday it would be playing a major role in Sunday’s game with F-16 fighters patrolling a temporary flight restriction zone over the stadium, in addition to ground troops, a flyover and other contributions, Politico reported.

Pentagon spokesman Army Col. Steve Warren told the website that while military flyovers have been cut back over the past year because of budget constraints, the Army will send helicopters to help open the Super Bowl.

"This is the Super Bowl," Warren said. "It’s an event of national prominence. We believe it benefits the U.S. military to provide this flyover."

A 24-hour FBI command center will monitor the latest counterterrorism intelligence, said Aaron Ford, head of the FBI's Newark office. Ford told WPIX-TV the effort is "an unprecedented collaboration" between 35 agencies.

Measures have been taken to protect power grids and to make sure there's plenty of backup energy in case of another blackout like the one last year at the game in New Orleans, said Jeffrey Miller, the NFL's head of security.

In Manhattan, the NYPD is drawing on its experience securing the annual New Year's Eve celebration in Times Square, the New York City Marathon, the U.N. General Assembly and other high-profile events to secure "Super Bowl Boulevard," a 13-block street fair on Broadway.

The department has deployed hundreds of extra uniformed and plainclothes police officers to the area. It's also relying on bomb-sniffing dogs, portable radiation detectors and a vast network of surveillance cameras to detect trouble.

On Friday, the FBI said it was investigating a suspicious powder mailed to several locations in New York and New Jersey, including at least five hotels near the site of Sunday's game.

The agency said further testing was being conducted on the substance, but it is "within normal values" and appeared not to be dangerous.

White powder also was found in a letter sent to former New York City Mayor Rudolph Giuliani's business in New York City, where police said preliminary tests showed it posed no threat.

A federal law enforcement official, who wasn't authorized to comment publicly and spoke on condition of anonymity, said powder from one envelope tested positive for baking soda. It's not clear where that letter was sent.

The Associated Press contributed to this report.