KABUL: Nearly a month after the September 11 attacks that killed 3,000 people, the United States launched its first major salvo in the “war on terror” by invading Afghanistan -- where, 15 years on, thousands continue to die each year.

Afghanistan, which the US invaded on October 7, 2001 in a bid to topple Al Qaeda hosts the Taliban, has become Washington's longest military intervention since Vietnam -- and the most costly, now crossing $100 billion.

The country remains wracked by insecurity as the resurgent Taliban dealt Afghan forces serious blows in 2015, the first year they led security operations in Afghanistan, taking over from Nato.

The militants continue to launch repeated attacks on urban centres, including an assault this week on the strategic northern city of Kunduz, while the capital Kabul is often rocked by bomb blasts. US military officials recently described the situation as a “stalemate”.

The Taliban threat forced President Barack Obama to slow plans to draw down US troop numbers at the end of this year. Some 8,400 will remain in the war-torn country in 2017, compared with 5,500 initially planned.

Here are some other key numbers charting the 15 years since the US invasion:

Civilians killed

A record 5,100 civilian casualties, including 1,600 deaths were recorded in the first half of 2016 according to the United Nations.

The previous year saw 11,000 deaths and injuries from attacks, mines and fighting between insurgents and government and foreign forces, which has spread to 31 of the country's 34 provinces. But the true human cost of these 15 years is impossible to establish because deaths of Afghans in the war's early years were not recorded.

Since 2009, the UN Assistance Mission in Afghanistan (UNAMA) has recorded 23,000 deaths and 41,000 wounded.

Foreign troops

The foreign military presence peaked at 150,000 deployed soldiers in 2012, of whom 100,000 were American. Most NATO troops withdrew from the country at the end of 2014, but Washington decided to keep 8,400 through 2017 to support local forces -- 350,000 soldiers and police, including 18,000 special forces.

Foreign military losses by the end of 2014 amounted to 3,500 killed and 33,000 wounded.

The breakdown included 2,400 dead and 20,000 wounded for the US; 453 and 7,500 for Great Britain; 159 and 1,859 for Canada; and 89 and 725 for France respectively-- figures that do not include private security contractors.

Afghan forces officially lost 5,000 men in 2015 including 3,700 police.

The money

The United States has spent around $110 billion on Afghanistan's reconstruction since 2001, more than the cost of the Marshall Plan that rebuilt a devastated Europe after World War II, but with limited results.

Some 80 per cent of that sum has landed in “American pockets” according to European observers in the form of military contracts, maintenance tasks and various consultants.

Corruption too has swallowed a large part. According to Transparency International, it is to blame for the state “failing to deliver basic services to citizens”.

The group ranks Afghanistan as the world's third most corrupt state.

Unemployment and displacement

Despite colossal amounts of foreign aid -- international donors at a conference in Brussels on Wednesday pledged $15.2 billion over the next four years -- reconstruction efforts are advancing at slow pace and the unemployment rate exceeds 40 per cent, according to the World Bank.

There are currently 1.2 million Afghans who are internally displaced, with the figure shooting up in 2013 because of increasing insecurity, according to Amnesty International.

Pakistan is hosting some 2.4 million Afghan refugees whom it is pressuring to leave and there are around one million in Iran, estimates say.

According to an estimate by the Norwegian Refugee Council and confirmed by authorities, 70 per cent of people living in major cities, including Kabul, reside in makeshift camps.