An image from the scene in Darna. (YouTube)

Video footage has emerged of an execution-style killing carried out by an Islamist militia in the eastern Libyan city of Darna. In a statement published Friday, human rights group Amnesty International decried the purported execution, which took place in a soccer stadium on Aug. 19, apparently "organized by an armed group called the Shura Council of Islamic Youth," and said the act was a sign of the Libyan government's "failure to prevent parts of the country from descending into violence and lawlessness."

Buried beneath the grim news of bloodshed further east in Gaza, Syria and Iraq, Libya's summer of chaos continues unabated. On Thursday, neighboring countries halted most flights to the country on security grounds after "unidentified warplanes," believed to belong to rogue general Khalifa Haftar, bombed targets in the capital Tripoli, Reuters reported.

The country's central government is toothless in the face of a hodgepodge of tribal and city militias as well as Islamist factions that have come to the fore since the 2011 toppling of Libyan dictator Moammar Gaddafi. Rival groups openly trade gunfire in daylight in Libya's coastal cities. In Darna, a traditional hotbed for jihadists, the Libyan state has virtually no footprint whatsoever, says Amnesty.

"There has been no police or army presence since [2011]," reads the statement, adding that the city's "Court of Appeals has been suspended since June 2013 following the assassination of a senior judge, amid repeated threats to judges by armed groups."

In the footage, which is available on YouTube, masked gunmen waving black flags bring a blindfolded Egyptian man identified as Mohammad Ahmad Mohammad onto the field in a pick-up truck. He is eventually shot in the head by a person dressed in civilian clothes, believed to be the brother of a man Mohammad is said to have killed. The murder is one of the starkest instances yet of Islamist groups enacting sharia law in the country. (Since Gaddafi's fall, Salafists have also set about attacking the shrines of Sufi saints.)

"This unlawful killing realizes the greatest fears of ordinary Libyans, who in parts of the country find themselves caught between ruthless armed groups and a failed state," said Hassiba Hadj Sahraoui, the organization's Middle East and North Africa deputy director, in Amnesty's press release.

Islamist groups are also vying for control in the nearby city of Benghazi as well as in Tripoli. In recent months, forces loyal to Haftar, a shadowy figure once deep inside the Gaddafi regime, have launched numerous strikes on Islamist positions in the country, though not with the support of the government, which Haftar earlier described as illegitimate.

The conflict has chased away foreign diplomats and businesspeople, and shuttered Tripoli's main airport, which is now a contested battlefield between rival militias. Libya's security crisis belies the hopes that surrounded the country in 2011, when a swift NATO bombing campaign allowed rebel units to defeat Gaddafi's forces (and eventually corner, capture and kill the dictator).

The mess that followed -- with the rebel alliance splintering and feuding militias calling the shots in various parts of the country --- shows how complicated regime change can be, especially when instigated by force of arms. The central government has no real standing army of its own and its elected officials are now meeting in the city of Tobruk, on the border with Egypt, instead of Tripoli or Benghazi, historic centers that are now war zones.