The UN Security Council called an emergency meeting after North Korea's launch of a long-range rocket, which Pyongyang said was carrying a satellite, but the US and its allies condemned as a missile test.
US Strategic Command said Sunday that its "systems detected and tracked what we assess was a North Korean missile launch into space ... the missile was tracked on a southerly launch over the Yellow Sea."
Pyongyang pronounced the mission a "complete success," after claiming the rocket managed to put an observation satellite into orbit.
State-run KCNA news agency showed a photograph of North Korean leader Kim Jong Un signing the order for the launch of the satellite, Kwangmyongsong-4.
A spokesman for UN Secretary General Ban Ki-moon called the action "deeply deplorable."
US Secretary of State John Kerry condemned it as "a flagrant violation of UN Security Council Resolutions," which prohibit North Korea from test-firing any rocket based on ballistic missile technology.
The US and its allies believe Pyongyang's move was a cover to test a ballistic missile capable of carrying a nuclear warhead.
The launch followed a nuclear test conducted by North Korea one month ago.
Kerry said this was the second time in just over a month that Pyongyang "has chosen to conduct a major provocation, threatening not only the security of the Korean peninsula, but that of the region and the United States as well."
South Korean President Park Geun Hye said, "North Korea has committed an unacceptable provocation of launching a long-range missile after conducting a fourth nuclear test," Yonhap news agency reported.
She demanded that the UN "quickly come up with strong sanctions."
A top South Korean defence official said that Seoul and Washington have agreed to begin talks on the likely deployment of an advanced missile defence system - Terminal High Altitude Area Defence - on South Korean soil, Yonhap reported, despite opposition from China and Russia.
Kerry reaffirmed Washington's "iron-clad commitment" to the defence of its allies, including Seoul and Tokyo, in the face of "this most recent destabilizing and unacceptable challenge to our common peace and security."
North Korea's chief ally, China, also criticized the launch, which came after Beijing's repeated warnings against inflaming geopolitical tensions.
"China expresses regret that North Korea, in spite of the pervasive opposition of the international community, insisted on using ballistic missile technology to carry out a launch," Foreign Ministry spokeswoman Hua Chunying said.
EU foreign policy chief Federica Mogherini condemned "yet another outright and grave violation" by North Korea of its "international obligations."
"These actions represent a direct threat to international peace and security in the region and beyond, and they further aggravate tensions on the Korean Peninsula to the detriment of all," Mogherini said in a statement.
She demanded Pyongyang "abandon its programmes to develop ballistic missiles, nuclear capabilities and weapons of mass destruction in a complete, verifiable and irreversible manner" and return to negotiations.
Russia slammed North Korea for disregarding warnings from the international community, and said its actions have caused a "dramatic aggravation of the situation on the Korean Peninsula and generally in North-East Asia."
Britain and France strongly condemned the launch, as did Germany, whose Foreign Minister Frank-Walter Steinmeier said, "This open challenge of the world community by North Korea must not remain without appreciable consequences."
In Pyongyang, the KCNA news agency quoted the National Aerospace Development Administration as saying the launch was "an epochal event in developing the country's science, technology, economy and defence capability by legitimately exercising the right to use space for independent and peaceful purposes."
In language typical of the North's propaganda machinery, it described the "fascinating vapour of Juche satellite trailing in the clear and blue sky in spring of February ... a gift of most intense loyalty presented by our space scientists and technicians to the great Comrade Kim Jong Un."
US National Security Advisor Susan Rice spoke earlier of "North Korea's determination to prioritize its missile and nuclear weapons programmes over the well-being of its people."
Japanese Prime Minister Shinzo Abe also called the launch "absolutely unacceptable."