The United States has carried out an air raid against Taliban fighters in Afghanistan, a US forces spokesman said a day after President Donald Trump spoke to a senior Taliban leader by phone.

"The US conducted an air strike on March 4 against Taliban fighters in Nahr-e Saraj, Helmand, who were actively attacking an ANDSF [Afghan National Defence and Security Forces] checkpoint," said Colonel Sonny Leggett in a tweet on Wednesday, adding that it was a "defensive strike".

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The raid, the first against the Taliban in 11 days, comes days after the US and Taliban signed a deal aimed at ending the nearly 19-year-old war in Afghanistan - the US's longest.

The Taliban leadership promised the international community it would reduce violence, Leggett said, referring to the deal signed in the Qatari capital, Doha, on February 29.

He said, however, the US was committed to peace but called on the Taliban to stop "needless attacks" and uphold their commitments.

According to Leggett, Taliban fighters had carried out 43 attacks on checkpoints in Helmand on Tuesday.

"In the past two days we have witnessed the most intense Taliban attacks in Helmand," Provincial police spokesman Mohammad Zaman Hamdard told AFP news agency:

"They have attacked several districts and many military bases," he added.

The Taliban had, earlier on Wednesday, killed at least 20 Afghan soldiers and policemen in a string of overnight attacks, government officials told AFP news agency.

"Taliban fighters attacked at least three army outposts in Imam Sahib district of Kunduz last night, killing at least 10 soldiers and four police," a member of the provincial council, Safiullah Amiri, said.

The Taliban also attacked police in central Uruzgan province on Tuesday night.

The violence has cast a pall on the nascent Afghan peace process, with the armed group clashing with Kabul over a prisoner exchange dispute before talks that are due to begin on March 10.

'Very good talk'

The agreement in Doha, which was finalised after more than a year and a half of negotiations, paves the way for the withdrawal of all US and NATO troops from Afghanistan and a commitment by the Taliban that Afghan territory will not be used to launch attacks on other countries.

President Trump on Tuesday said he held a "very good talk" with a Taliban leader in what may be the first direct discussion between a US leader and a senior Taliban official.

Taliban's chief negotiator, Mullah Abdul Ghani Baradar, and Trump held a 35-minute telephone call, a Taliban spokesman said, with Trump later confirming the call to reporters at the White House.

In an emailed statement later, Taliban spokesman Zabihullah Mujahid said Trump told Baradar that US Secretary of State Mike Pompeo would soon speak to Afghan President Ashraf Ghani "so that the barriers against the inter-Afghan talks get removed".

At least three people were killed on Monday in a football stadium blast in Khost province after President Ghani rejected prisoner swap deal that would see the release of 5,000 Taliban prisoners.

The Taliban has said it will not begin talks with the Afghan government as envisaged in the agreement until the prisoner release takes place.

The Afghan Independent Human Rights Commission expressed concern about the prisoner release in a letter to US officials, the Taliban and the Afghan government.