* Coalition troops in Afghanistan engage Taliban insurgents
* Spokesman says they were acting in self-defence
* Thousands of government forces at Kunduz airport
* Reinforcements delayed by Taliban spoiling tactics
* Parliamentarians call for president to resign (Adds U.S. special forces involvement and air strikes)
By Hamid Shalizi and Kay Johnson
KABUL, Sept 30 (Reuters) - U.S. and allied special forces in Afghanistan battled insurgents besieging the airport outside the northern city of Kunduz that was captured by the Taliban this week, a coalition spokesman and Afghan official said on Wednesday.
It was the first report of on-the-ground clashes between Taliban militants and foreign troops supporting their Afghan allies during three days of sometimes heavy fighting for control of the strategic city of 300,000.
Kunduz is the first provincial capital to fall to the Taliban since the hardline Islamist movement was toppled from power in 2001.
The swift re-taking of the city promised by President Ashraf Ghani has failed to materialise, as Taliban fighters dig into positions around the city and mine roads to prevent reinforcements from reaching weary Afghan forces.
They have also placed large containers across streets to further limit people’s movement in and out of Kunduz, said Ahmad Sahil, a local television producer who was inside the city.
In another setback for the government, nearly 200 Afghan security personnel abandoned Bala Hissar hill, an outpost in Kunduz that overlooks the city’s main roads, after running out of ammunition and food, said an Afghan security official.
Troops fled the strategic position in pick-up trucks and Humvees. Dozens headed for shelter at Kunduz airport, where thousands of police and soldiers have already retreated in the last two days of fighting.
To the south, in neighbouring Baghlan province, a group of 800 Afghan troops on its way to reinforce Kunduz repelled a Taliban ambush and was waiting for bomb squads to clear the road into the city, said Afghan army officer Sayed Ahmad Mujahid.
They had only advanced about one kilometre during the day, he added.
Afghanistan’s intelligence agency said in a statement issued late on Tuesday that an air strike had killed Mullah Abdul Salam, the Taliban’s shadow governor for Kunduz province, and 15 others on the outskirts of the airport.
It was not possible to verify the report independently, and the Taliban denied the claim, later releasing what they said was an audio statement from Salam recorded on Wednesday.
At least five U.S. air strikes have targeted Taliban positions near the city since the fighting broke out on Monday.
Coalition special forces including U.S. troops, while advising Afghan troops operating in the vicinity of the Kunduz airport, “encountered an insurgent threat” at about 1 am on Wednesday, according to a statement from NATO.
Coalition spokesman Col. Brian Tribus gave few details about the foreign troops’ engagement with insurgents while supporting Afghan forces overnight.
He confirmed special forces fought the insurgents, but added: “This was done out of self-defence. When they encountered the threat, they defended themselves.”
A senior Afghan security official said about 100 members of U.S. special forces fought off Taliban attackers threatening to breach the airport in the early hours of Wednesday.
The heavily armed troops, wearing night-vision goggles, left the airport and killed the assailants before returning, added the official, who spoke on condition of anonymity.
An undisclosed number of coalition troops were dispatched to Kunduz this week to support the Afghan army.
“They are in a non-combat role. That said, they also maintain the right to defend,” Tribus said of the coalition forces.
NATO had more than 100,000 troops in Afghanistan at its peak, but most had withdrawn by the end of 2014 and the far smaller mission now is designed to “train, assist and advise” local forces.
In Kabul, Afghan lawmakers called on Ghani to resign over his government’s “shameful” handling of the battle, the latest blow to the leader whose first year in office has been marred by political infighting and escalating violence.
“It is shameful how they (the government) have dealt with the situation in Kunduz,” said Iqbal Safi, a member of parliament from Kapisa province, during a televised session of parliament.
“Ghani and Abdullah must step down,” he added, referring to Ghani’s Chief Executive Abdullah Abdullah.
Sayed Zafar Hashemi, Ghani’s deputy spokesman, said it was parliamentarians’ right to protest.
“For the president, the first priorities are the safety of the citizens in Kunduz and clearing the area of terrorists.”
Despite assurances by the Afghan government that progress was being made in Kunduz, the lack of reinforcements and the Taliban’s aggressive tactics point to a potentially long and bloody fight.
Wahidullah Mayar, a spokesman for the Public Health Ministry, said on Twitter that 30 people had been killed and more than 200 injured in Kunduz fighting.
“Around 90 percent of them are civilians,” he said.
Many civilians fled during the surprise attack early on Monday, but thousands remain trapped. (Additional reporting by Mirwais Harooni, Abdul Aziz Ibrahimi and Jessica Donati in KABUL; Writing by Krista Mahr; Editing by Mike Collett-White)