UNITED NATIONS, Sept. 23 (Xinhua) -- Streets near the UN General Assembly venue on Tuesday teemed with law enforcement and their weapons, security craft bobbed in the neighboring East River and the sky above was patrolled by helicopters and drones.

Stephane Dujarric, chief spokesman for UN Secretary-General Antonio Guterres, has said that 193 delegations representing the total UN membership are expected to attend the general debate of the 80th session of the UN General Assembly.

Dujarric said the delegations include approximately 89 heads of state, five vice presidents, one crown prince and 43 heads of government. About 1,642 bilateral meetings have been scheduled in the lobby of the General Assembly building.

While officials said there was no known specific threat targeting the United Nations, security was ramped up out of an abundance of caution.

"Designated a National Special Security Event, or NSSE, this is the largest gathering of global leaders on the planet," said Matt McCool, special agent in charge of the New York field office of the U.S. Secret Service.

New York City Police Commissioner Jessica Tisch said the New York Police Department (NYPD) security operation involves hundreds of motorcades throughout the week.

She said that the officers supporting the motorcades are fully briefed on the respective countries, including security concerns and any unique cultural or diplomatic considerations. Beyond the UN Headquarters itself, other meetings and special events across the city require resources and protection.

The commissioner said the Jewish holiday of Rosh Hashanah is being observed this week, necessitating stepped-up security at synagogues.

The NYPD was also tasked with policing demonstrations and keeping opposing protestors from each other.

Tisch said that thousands of NYPD officers secure motorcade routes, fortify protection for the president of the United States, support security at hotels where heads of state stay and ensure the safe movement of delegations citywide.

"The resources that we are deploying are extensive and go beyond just a uniformed presence," said Tisch.

As for the UN Headquarters, she said, "Our specialized units will be out in full force all week, including harbor units on the rivers, aviation assets overhead, heavy weapons teams and counter-terrorism officers on the street and our Technical Assistance Response Unit drone team will be providing real-time situational awareness."

She said there is a temporary flight restriction for a 2-nautical-mile (3.7km) radius around the United Nations campus on Manhattan's East River for the duration of the meetings.

McCool said the Secret Service would join the NYPD in flying drones in the restricted airspace. There will also be waterway restrictions along the East River, with the U.S. Coast Guard and the NYPD harbor unit enforcing restrictions. There are no-go areas on the water and on the streets.

On the ground, checkpoints leading to the UN Headquarters feature electrically or hydraulically operated "wedge barriers" with steel plates that can be lowered for vehicle access.

Checkpoints are surrounded by a dozen or more officers from various law enforcement agencies, armed with weapons ranging from those worn on the hip or in a shoulder holster to long guns slung barrel-down from bullet-proof vests. ■