Media playback is unsupported on your device Media caption The execution of Chang Song-thaek shows no-one is immune in North Korean politics, says the Lucy Williamson

The US has urged Pyongyang to avoid any provocative acts following the execution by North Korea of a once-powerful political figure.

North Korea announced on Thursday that it had executed Chang Song-thaek, the uncle of leader Kim Jong-un, for "acts of treachery".

The move has raised concerns of instability in the secretive and repressive nuclear-armed country.

The US said it was consulting its regional allies.

Removing a single individual may not be enough to quell dissent if it is widespread Dr John Swenson-Wright, Chatham House Brutal but risky moveFive infamous purges

State Department spokeswoman Marie Harf said she would not speculate on what might be happening within the North Korea regime, but that the execution of Mr Chang had been "an incredibly brutal act" which "underscores the horrific human rights record of the North Korean regime".

"We're going to increase our discussions with our allies and partners in the region about the internal situation in North Korea," Ms Harf told reporters in Washington.

"North Korea has a choice between continuing down the path of isolation and impoverishment of its own people or meeting its obligations and coming back to the international system," said Ms Harf.

She said the US "would urge the North Koreans not to take provocative acts" as it was "not in the interest of regional stability".

Image caption The execution was given widespread coverage in North Korea's state-run media

Image caption Chang Song-thaek had often been seen at Kim Jong-Un's side

International talks aimed at convincing the North to denuclearise and reduce its threatening posturing towards the international community in exchange for aid have repeatedly failed.

'Worse than a dog'

Mr Chang was married to the sister of late leader Kim Jong-il, and is believed to have mentored Kim Jong-un when he succeeded his father in North Korea in 2011.

He had been seen as the second-most important figure in the country, holding several key posts, but this week was dramatically removed from a special party session by armed guards and stripped of all his titles.

Media playback is unsupported on your device Media caption State TV in North Korea announced the execution of a "wicked political careerist"

On Thursday, the state news agency KCNA said he had admitted at a military trial to trying to overthrow the state, and had been executed immediately.

A long and detailed statement described him as "despicable human scum... worse than a dog".

Two of his closest aides had already been executed, and many of his subordinates and allies have reportedly been recalled to Pyongyang.

Correspondents say the speed and and brutality of Mr Chang's case has been startling. Political purges are common, but the regime rarely makes such an exhibition of senior figures who fall from grace.

However, analysts say the purge is bound to raise regional tensions.

South Korean President Park Geun-Hye has warned the North is "engaged in a reign of terror" aimed at consolidating Kim Jong-un's grip on power. The South's military has said it is on heightened alert.

South Korean Unification Minister Ryoo Kihl-jae warned the purge could be followed by military moves from Pyongyang - including another nuclear test. Military action is often used by the North as a way of curbing internal agitation.

Chang Song-thaek Born 1946; marries Kim Jong-il's sister in 1972

Joins Korean Workers' Party administrative ranks in 1970s

Elected to Central Committee in 1992

Sidelined in 2004, but rehabilitated in 2006

2011: Gets top military post under Kim Jong-un

Nov 2013: Dismissed from his position

December 2013: Executed as a "traitor" Profile: Chang Song-thaek Secretive 'first family' What is known about the purge?

In February it carried out its third nuclear test, to widespread international condemnation, and threatened attacks on Japanese, South Korean and US military targets in the region.

Japan said it was "closely watching" the latest situation, and would remain in communication with its neighbours on the matter, Kyodo news agency quoted Chief Cabinet Secretary Yoshihide Suga as saying.

China - Pyongyang's only ally and major trading partner - described Mr Chang's execution as an "internal matter".

"As a neighbouring country, we hope for North Korea to maintain stability..." a foreign ministry spokesman said.

Mr Chang made a high-profile trip to China in 2012 where he met then-President Hu Jintao, and signed a raft of economic deals, including the development of two special economic zones.

The BBC's Lucy Williamson in Seoul says one theory for Mr Chang's downfall is that he was too keen an admirer of China's economic reform.

The speed of his downfall has sent a powerful message to those who had hoped for change under North Korea's new leadership that he can crush any opponents, says our correspondent.

But many will be asking whether it is his nephew's hand alone behind this execution, or whether the army is seeking to reassert its power, she adds.