KABUL, Afghanistan -- Two American-made UH-60 Black Hawk helicopters arrived in Afghanistan on Monday, the first of nearly 160 such aircraft that the country's air force will get in the coming years as part of an ongoing modernization plan.
NATO has repeatedly stressed that building a modern, sustainable air force is vital for the Afghans to counter Taliban insurgents, who have made substantial gains in recent years.
The Black Hawks will eventually replace an aging fleet of Russian-made Mi-17 helicopters, which are used to transport troops and supplies, perform medical evacuations and provide close air support.
The Black Hawks will make the Afghan force more "capable and sustainable," NATO's Resolute Support mission said in a tweet on Monday.
The initial two aircraft, which were unloaded at Kandahar Air Field, will be used for training, as will two additional Black Hawks to be delivered on Oct. 23, Resolute Support said. A total of 159 Black Hawks are expected to be delivered between now and 2023.
The United States initially bought Mi-17s for the Afghans to speed development of their fledging air force, which has used earlier versions of the helicopter since the 1970s.
But in 2013, under pressure from Congress, the Pentagon blocked a purchase of more than $1 billion worth of new Mi-17s. The following year, after Moscow's military involvement in Syria and Ukraine, President Barack Obama issued restrictions on doing business with Russian arms manufacturers.
The Pentagon predicts Afghanistan's battle-worn Mi-17 fleet will become unsustainable by the middle of next year, largely because of lack of parts and aging airframes. It requested funds from Congress in November to modify older-model Black Hawks to enable them to perform the tasks of the Mi-17s.
Critics have said the push to replace the Russian aircraft with American models has been motivated primarily by politics. They fear a disruption caused by the switch -- at a time when the Taliban are said to be stronger than at any other point since 2001 -- could further benefit the insurgents.
U.S. military officials have offered assurances that any disruption would be minimal and that the Black Hawks, which U.S. forces already use in Afghanistan, are superior to the Mi-17s.
Training for the Afghans on the Black Hawks is scheduled to start next month in Kandahar and at Fort Rucker in Alabama. Mi-17 pilots could be ready to fly Black Hawks with as little as 12 weeks of instruction, according to the Pentagon's estimates.
Gen. Mohammad Radmanish, deputy spokesman for the Afghan Defense Ministry, said Afghan forces were excited to start the Black Hawk program after many months of anticipation.
"After we get all the helicopters and our forces get trained, I believe it will help us a lot in the fight against terrorism," Radmanish said.
Zubair Babakarkhail contributed to this report.