The Taliban overran three security checkpoints in Afghanistan's northern Takhar province, killing eight policemen and cutting off a key road and two of the region's districts, an Afghan official said on Tuesday.

According to provincial spokesman Sunatullah Timor, the attack on Monday's triggered hours of firefighting, leaving three police officers wounded. Eight of the attackers were also killed in the gun battle, he added.

The insurgents succeeded in cutting off the districts of Darqad and Khuja Bhawedin, Timor said, but the government has sent in reinforcements and launched a counter-attack.

The attack coincided with Monday's visit to Kabul by US Defence Secretary Jim Mattis to assess what has become America's longest war as the Trump administration weighs sending in more United States troops to help the Afghans fight the insurgency.

From Kabul, Mattis offered a grim assessment for Afghan forces fighting the Taliban, saying that “2017 is going to be another tough year.”

Mattis also accused Russia of providing weapons to the Taliban for use against American-backed forces in Afghanistan — a charge Moscow denies.

Just last week, a Taliban raid on an Afghan base left an estimated 130 soldiers and military personnel dead.

Explore: Over 100 killed, wounded in Taliban attack on Afghan military base

Mattis met with Afghan President Ashraf Ghani and other senior government officials just hours after the nation's defence minister and army chief resigned over the massacre.

The attack — the biggest ever on a military base in Afghanistan — involved multiple gunmen and suicide bombers in army uniforms who penetrated the compound of the 209th Corps of the Afghan National Army in northern Balkh province on Friday, killing and wounding scores.

Also on Monday, a suicide bomber driving a minivan struck a checkpoint in eastern Khost province, killing at least four Afghan security guards.

Gen Faizullah Ghyrat, a provincial police chief in Khost, said that six other security guards were also wounded in the attack.

The guards were providing security for a US military base called Camp Chapman near the city of Khost, said Ghyrat.

On Tuesday, in a statement sent to the media, Taliban spokesman Zabihullah Mujahid claimed responsibility for the attack in Khost.

Explore: Afghan govt ready to negotiate with Taliban unconditionally, says envoy

The Taliban have stepped up their attacks against both Afghan forces and civilians since foreign combat troops pulled out of the country at the end of 2014, leaving only an advisory and training contingent of international forces behind.

The Afghan military and security forces, with 195,000 soldiers and more than 150,000 policemen, have struggled in fighting the insurgency on their own.