Police in Nepal's capital Kathmandu have launched a campaign to round up cows roaming the streets, blaming the sacred animals for car accidents and traffic jams.

"The stray cows and oxen have been a big nuisance in Kathmandu streets. They not only cause accidents, but also make the streets untidy," Pawan Giri, spokesman for the Kathmandu Metropolitan Traffic Police, told AFP.

"We see traffic jams because the drivers who try to avoid the cows often crash into other vehicles."

He said the captured animals would be detained until their owners paid a fine of approximately $60 for their release.

Cows are a regular sight in the smog-choked capital and are often found eating from piles of garbage on the roadside.

Regarded as an incarnation of the Hindu Goddess of prosperity Laxmi, the beasts are treated as sacred in Nepal, where the majority of the population is Hindu.

During the annual Tihar festival in the autumn, Hindus spend a day worshipping them by offering food and gifts.

The traffic police say they have rounded up 18 animals since launching the operation Monday and they plan to continue this drive for several weeks.

While the abolishment of a Hindu monarchy in 2008 launched a secular era, Nepalese authorities still routinely arrest people for killing cows, mainly in rural areas.

Cow slaughter remains illegal in Nepal and can carry a prison sentence of up to 12 years.