NEW YORK – New York City Mayor Bill de Blasio said Sunday that residents of the city would see an expanded presence of police as officials investigate a bombing in Chelsea that injured 29, while guarding the United Nations General Assembly, which draws leaders from around the world to New York each year.

“You will see a very substantial NYPD presence this week, bigger than ever,” de Blasio said during a press conference just after noon Sunday.

De Blasio said all 29 victims of the explosion, which rocked a crowded and popular Manhattan neighborhood, have been released from area hospitals. Another possibly-explosive device discovered blocks away was safely removed early Sunday.

Officials said there’s no evidence currently linking the explosion to terrorism, and said the incident appeared to be unrelated to a pipe bomb explosion earlier Saturday in Seaside Park, New Jersey near the start line of a charity run.

“We know from everything we’ve seen so far that this was an intentional act. Again we do not know the nature of it, we do not know the motivation,” de Blasio said.

At a press conference earlier on Sunday morning, New York Governor Andrew Cuomo said he had spoken with New Jersey Governor Chris Christie, and so far the explosives did not appear to be similar.

Atlhough Cuomo on Sunday referred to the explosion as an act of “terrorism,” NYPD, FBI and other NYC officials were hesitant to use the phrase until a suspect or motive could be established.

During the U.N. General Assembly, New York typically increases police presence, but officials said Sunday law enforcement would be on particularly high alert in the city this week, as a result of the explosion.

Cuomo said 1,000 additional law enforcement officers were being deployed after the Saturday night blast in Chelsea, a primarily residential neighborhood on Manhattan’s west side that’s known for its art galleries and large gay population.

Stephane Dujarric, Spokesman for the U.N. Secretary General, told CBS News’ Pamela Falk that more than 14,000 passes have been issued for dignitaries, their aides, and additional press for the U.N. General Assembly this year.

“Security inside the United Nations is being assessed on a constant basis. Outside of the UN, security is the responsibility of the host country. We receive great cooperation and appreciate the support from the federal authorities and the NYPD throughout the year, and especially during the General Assembly to keep staff, delegates and visitors safe,” Dujarric said.

It was unclear who was behind the blasts in New York and New Jersey, and what motivated them. A law enforcement source tells CBS News senior investigative producer Pat Milton that while no suspect nor motive has been established, terrorism has not definitively been ruled out as a possibility.

The second device that officers investigated four blocks from the Chelsea scene was a pressure cooker with a cellphone and wires attached, and was found in a plastic bag. The device was removed with a robot and taken to a department firing range in the Bronx.

New York Police Commissioner James O’Neill said at Sunday afternoon press conference that a bomb squad was still investigating the device.

The New York Times reports the second device appeared to be similar to the devices used in the Boston Marathon bombing.

The explosion that rocked a bustling Chelsea neighborhood appeared to have come from a construction toolbox in front of a building. Photos from the scene show a twisted and crumpled black metal box.

“This is a very dense area, the whole block is restaurants and residences and this area on a warm Saturday night is an area swarming with people,” New York City Councilman Cory Johnson told CBS New York.

The blast happened on West 23rd Street, in front of a residence for the blind, near a major thoroughfare with many restaurants and a Trader Joe’s supermarket. Witnesses said the explosion at about 8:30 p.m. blew out the windows of businesses and scattered debris in the area. Officials said no evacuations were necessary.

New York City subway routes were affected by the explosion, which rattled some New Yorkers and visitors on the heels of the 15th anniversary of the 9/11 terror attacks. Cuomo said mass transit in the area would resume as early as Monday.