The bomb went off as people made their way into a central mosque for prayers in Herat. Local media reports say at least 10 were killed and the death toll may increase.
A bomb blast has killed at least seven people and wounded 15 others outside a mosque in Afghanistan's western city of Herat on Tuesday, said Afghan police.
Local media reports put the death toll at 10.
Abdul Ahad Walizada, spokesman for the Herat police, said the bomb went off as people made their way to the mosque for prayers.
Officials said the explosives were hidden in a motorcycle left in a parking area outside the Jama Masjid, a large mosque dating from the 12th century.
They feared the death toll could rise.
Near the border with Iran, Herat is one of Afghanistan's largest cities.
Rocket hits Indian diplomatic compound
In another incident of violence, a rocket struck an Indian diplomatic compound in Afghanistan's capital Kabul on Tuesday, police said, adding no one was injured in the attack.
The rocket hit a tennis court, a kilometre or so away from a venue where representatives of about two dozen international delegations met to discuss efforts to end violence.
Sirens and warnings of "incoming" missiles sounded in a number of embassies, followed by a dull thump as the rocket exploded.
The attacks came after a spate of violence in Kabul.
On May 31, a huge truck bomb detonated outside gates leading to the fortified area, killing more than 150 Afghans and wounding hundreds.
That blast caused serious damage to the German embassy, and lighter damage to the Indian and other embassies nearby.
Several protesters were killed in clashes with police on Friday at the bomb site, and at least a dozen people were killed when suicide bombers attacked the funeral for one of the dead protesters on Saturday.
A bomb attack on the Indian embassy in 2008 killed more than 40 people.