NEW YORK -- As the prospect of a Taliban takeover in Afghanistan's south looms, with three provincial capitals under attack by the insurgents, the escalating violence spurred by the U.S. withdrawal is being felt across the war-torn country.

On Tuesday, a bombing near Kabul's heavily fortified "Green Zone" killed at least three and injured seven in a busy market square. A government spokesman said the attack was meant to target a senior Afghan government official.

The explosion occurred soon after a phone call between U.S. Secretary of State Antony Blinken and Afghan President Ashraf Ghani, who agreed on the need to speed up the stalled peace talks with the Taliban and condemned ongoing attacks by the insurgents, the U.S. State Department said.

The call took place after Ghani criticized the Americans over the weekend for what he called a "hasty withdrawal" that was leading to the Taliban's rapid gains.

The Americans followed the Kabul bombing with a grim warning: the prospect of civil war. U.S. State Department spokesman Ned Price said that, if the Taliban undermine peace talks, "they will be an international pariah... and the concern on the part of all of us, one of the main one of many concerns, is that the result will be civil war."

On the ground, taking more territory under their control is placing the Taliban in a more advantageous position in the stalled talks.

"At this point, they [the Taliban] are demanding that they take the lion's share of power in the next government given the military situation as they see it," Zalmay Khalilzad, the American envoy for Afghan reconciliation, said at the Aspen Security Forum on Tuesday.

With the U.S. military withdrawal from Afghanistan almost complete, and the Pentagon reporting that over 95% of the "retrograde" is done, the military situation has deteriorated from the perspective of Kabul and Washington.

The Taliban and their supporters have "strategic momentum" and already control about half of the country's 400 districts, according to Gen. Mark Milley, chairman of the U.S. Joint Chiefs of Staff.

Crucially, the insurgents are now poised to take over three major cities in the country's southern belt: in the southeast, Kandahar, capital of the province of the same name, known as the medieval capital of Afghanistan, the spiritual capital of the Pashtuns and the birthplace of the Taliban; in the south, Lashkar Gah, the provincial capital of the vast Helmand province; and in the west, Herat, capital of the province of the same name, which borders Iran. The insurgents have already taken over international border crossings with Pakistan, Iran and Tajikistan.

The Associated Press reports that the Taliban have captured nine out of the Lashkar Gah's 10 districts, and government forces have asked the city's 200,000 residents to evacuate. The fighting is intense, with regular Afghan troops dug in, aided by U.S. airstrikes as well as special forces commandos flown in from Kabul. It is unclear whether the U.S. air campaign is being conducted from forces still in Afghanistan or from American naval assets in the Arabian Sea.

Social media images from residents show that the Taliban have entered parts of the city as well as people's homes, while the insurgents reportedly now control the city's television and radio stations. If it falls to the Taliban, Lashkar Gah be the first provincial capital captured by the Taliban in 20 years.

The other two cities under attack by the Taliban are seeing similar air support for Afghan forces by the Americans, according to the AP. In Herat, which over the weekend looked like it would fall, Afghan forces have pushed the Taliban back and reopened the local airport. But Kandahar remains under siege, and the Taliban have managed to attack the airport, forcing it to close.

A sniper keeps a watch from the roof of the parliament building in Kabul before Afghan President Ashraf Ghani arrives on Aug. 2.   © Reuters

This push for capturing part of what demographers call the Afghan section of the "Pashtun Crescent" that runs between Pakistan and Afghanistan suggests a change of strategy by the Taliban.

"At this stage of the conflict, top Taliban elites might see a proto-state with one or more provincial capitals in this part of Afghanistan to be a source of major political and material benefits," said Asfandyar Mir, a counterterrorism expert at Stanford University's Center for International Security and Cooperation.

In the early phases of the U.S. military withdrawal, announced in April by U.S. President Joe Biden, the Taliban were taking sparsely populated and remote districts, where Afghan forces either quickly surrendered or were overwhelmed by the insurgents. But as the peace talks with the government of President Ghani failed, and calls for a cease-fire were ignored by both sides, the Taliban took the fight to urban centers.

"Initially it appeared they only wanted to put pressure [on the provincial capitals] but now there appears to be a shift in strategy and Taliban are looking to capture them," said Mir, adding that the cities have major political value for the Afghan government and the Taliban.

"From the government's perspective, Kandahar and Herat are among the largest cities after Kabul and symbols of the government's political hold in the south and west respectively. For the Taliban, Kandahar and Lashkar Gah are the crown jewels of the base of their insurgency and perceived as significant by the south-dominated Pashtun political leadership. There is also the large-scale drug trade in this part of the country, which the Taliban tax and generate revenues from."