At least 22 police officers were killed in a Taliban ambush in western Afghanistan, a health official said on Monday, in another blow to Afghan forces already suffering record casualties.

The attack on the police convoy in Farah province follows a wave of violence across Afghanistan in recent weeks, including a suicide bombing inside an army base mosque on Friday, and intensifying efforts to convince the Taliban to end the 17-year war.

At least two police officers were wounded in Sunday's ambush, said Shir Ahmad Weda, director of the public hospital in the provincial capital.

The Taliban claimed responsibility for the attack in a WhatsApp message, saying 25 police were killed and four wounded.

"Four vehicles were destroyed and a large quantity of weapons were seized," Qari Yousuf Ahmadi, a spokesman for the militants, added.

Provincial police spokesman Mohibullah Mohib said the convoy had been travelling from Farah city to Juwain district when it came under attack.

Mohib put the death toll at five with another seven wounded.

Afghan government and military officials often downplay the casualty toll of security forces, while the Taliban frequently exaggerates the number its fighters have killed or wounded.

The Taliban and its smaller rival the militant Islamic State group (IS) have been inflicting record casualties on local forces this year.

At least 27 soldiers were killed in Friday's suicide attack in a mosque on an army base in the eastern province of Khost.

IS claimed responsibility for the explosion, which also wounded at least 79 service members.

That came days after a suicide assault on a religious gathering in Kabul that killed at least 55 people and wounded 94.

Since the start of 2015, when local forces took over from US-led Nato combat troops to secure the country, nearly 30,000 Afghan soldiers and police have been killed, President Ghani revealed this month — a figure far higher than anything previously acknowledged.

Experts have warned the attrition rate is unsustainable.

US envoy Zalmay Khalilzad expressed hopes in Kabul earlier this month that a peace deal to end the war could be struck before the Afghan presidential election, scheduled for April 20.

His comments underscore an apparent increasing sense of urgency in the White House and among American diplomats for such a deal to be done quickly.

But Afghan election organisers on Monday said they were considering delaying the poll for three months amid fears the ballot could derail efforts to persuade the Taliban to talk.