By Ju-min Park and David Brunnstrom
SEOUL/WASHINGTON (Reuters) - North Korea test-fired what appeared to be two intermediate range ballistic missiles on Thursday, but both failed, the U.S. military said, in a setback for North Korean leader Kim Jong Un ahead of next week's ruling party congress.
The isolated nation has conducted a series of missile launches in violation of U.N. resolutions ahead of the Workers' Party congress which begins on May 6. South Korea also says North is ready to conduct a new nuclear test at any time.
China said the U.N. Security Council was working on a response to North Korea's latest missile tests, while U.N. Secretary-General Ban Ki-moon urged Pyongyang to cease "further provocative actions."
Thursday's tests looked to have been hurried, according to a defense expert in Seoul, and follow a failed launch of a similar missile earlier this month.
The first launch, at about 6:40 a.m. local time (05:40 p.m. EDT Wednesday) from near the east coast city of Wonsan, appeared to have been of a Musudan missile with a range of more than 3,000 km (1,800 miles) which crashed within seconds, a South Korean defense ministry official said.
Later, at around 7:26 p.m., the North shot a similar intermediate range missile from the same area, but the launch was also understood to have failed, the official added.
The U.S. military's Strategic Command said it tracked two attempted launches, neither of which posed a threat to North America.
"Initial indications reveal the tests were not successful," said Lieutenant Colonel Martin O'Donnell, a STRATCOM spokesman..
The Musudan missile theoretically has the range to reach any part of Japan and the U.S. territory of Guam. It has never been successfully flight-tested.
A similar missile launched on the April 15 birthday anniversary of Kim's late grandfather, North Korea's founder Kim Il Sung, exploded in what the U.S. Defense Department called a "fiery, catastrophic" failure.
Some experts had predicted that North Korea would wait until it figured out what went wrong in the previous launch before attempting another, a process that could take months.
Yang Uk, a senior research fellow at the Korea Defence and Security Forum and a policy adviser to the South Korean navy, said the North Koreans appeared to be in a rush to demonstrate a success head of the party congress.
"They need to succeed but they keep failing," he said "They didn't have enough time to fix or technically modify the system, but just shot them because they were in a hurry."
U.S. and South Korean officials have expressed concerns that North Korea could attempt a fifth nuclear test in a show of strength ahead of the congress.
"Signs for an imminent fifth nuclear test are being detected ahead of North Korea's seventh Party Congress," South Korean President Park Geun-hye said at a national security meeting on Thursday.
The 15-member U.N. Security Council met to discuss the latest missile tests at the request of the United States. China's U.N. Ambassador Liu Jieyi, president of the council for April, said: "We're looking at a response from the Security Council."
Diplomats said the council was likely to issue a statement condemning the latest missile tests.
Japan's U.N. Ambassador Motohide Yoshikawa, also a council member, said that during the closed-door meeting "everybody condemned the latest failed launches."
Ban's spokesman, Stephane Dujarric, called the actions "extremely troubling."
Yonhap said the first missile was not detected by South Korean military radar because it did not fly above a few hundred meters, and was spotted by a U.S. satellite.
On Saturday, North Korea tested a submarine-launched ballistic missile, which traveled about 30 km (18 miles) off its east coast.
The tests have come in defiance of U.N. Security Council sanctions which were strengthened after North Korea's last nuclear test in January and a space rocket launch the following month.
(Editing by Mike Collett-White and Alistair Bell)