The UN voiced "serious concern" about the Taliban's persistent threat after the group killed seven people in two suicide attacks in Kabul Thursday, including one targeting a play at a French-financed high school.

The warning comes with the Afghan capital having been hit by a series of deadly attacks in recent weeks, highlighting the fragility of security as foreign combat troops leave after more than a decade of war.

The late afternoon bombing at the Istiqlal High School, attached to the city's long-established French cultural centre, killed a foreign national and came just hours after another suicide attack on a bus carrying Afghan troops in the capital's suburbs killed six soldiers.

The bomber killed a foreign national and wounded at least seven people, according to Kabul police official General Farid Afzail, who added that the perpetrator is thought to have been a teenager.

French Foreign Minister Laurent Fabius, however, said the "barbaric" attack had left several people dead.

The United Nations Security Council issued a unanimous statement condemning the attacks which also voiced "serious concern at the threats posed by the Taliban, Al-Qaeda and other terrorist and extremist groups, and illegal armed groups."

The blast struck during a musical theatre production entitled "Heartbeat: The Silence After the Explosion", which was a condemnation of suicide attacks, the BBC reported.

Taliban spokesman Zabihullah Mujahid claimed both bombings in separate email statements, saying the theatre show was "desecrating Islamic values" and "propaganda against jihad".

Witnesses described scenes of panic after the blast, with audience members screaming for help in the theatre hall filled with smoke.

The cultural centre is in the centre of Kabul, not far from the presidential palace and shares its grounds with the Istiqlal school, a French-financed institution that has taught generations of Afghan children.

Originally opened in 1970, the cultural centre was forced to close between 1983 and 2002 as Afghanistan was torn apart by a series of wars. It reopened in 2003 and was revamped in 2010.

French President Francois Hollande condemned the bombing as "heinous" and said it was an assault on "culture and creativity."

In the earlier attack, the bomber who was on foot targeted a bus carrying Afghan troops in Tangi Tarakhil on the outskirts of the capital, Afzail told AFP.

"As a result of the (first) attack, six Afghan army staff were martyred and 10 others were wounded," the general said.

A statement from the defence ministry confirmed the death toll, but said 11 people were wounded.

A recent spate of attacks in Kabul has seen militants target foreign guest houses, embassy vehicles, US troops and Afghan army buses over the past month.

The bloodshed has undermined claims that the insurgency is weakening as NATO's 13-year war ends, and heightened concerns Afghanistan could trip into a spiral of violence when the US-led military presence declines.

NATO's force in Afghanistan will change on December 31 from a combat mission to a support role, with troop numbers cut to about 12,500 -- down from a peak of 130,000 in 2010.

US Defense Secretary Chuck Hagel said on a visit to Kabul at the weekend that the upsurge showed "that the international community must not waver in its support for a stable, secure, and prosperous Afghanistan".

Hagel insisted Afghanistan would not go the way of Iraq, where another US-trained army virtually collapsed in the face of an onslaught by Islamic State jihadists after American troops left the country in 2011.

But a day later, Afghanistan's chief executive Abdullah Abdullah told Britain's Sunday Times newspaper that Western forces were leaving prematurely.

The attacks came as Washington announced it no longer held any prisoners in Afghanistan, a day after a damning US Senate report on the brutal treatment of "war on terror" detainees.

Afghan President Ashraf Ghani gave a stern condemnation of the CIA torture detailed in the report, saying it violated "all accepted norms of human rights" and was part of a vicious cycle of violence. (AFP)