Pakistan has arrested 20 Indian fisherman for violating the territorial waters of the country, its maritime security agency said Sunday.

The Indian fishermen were arrested and brought to the Southern city of Karachi early Sunday morning. Their boats were also seized. 

"We are preparing documents to produce all of them in court tomorrow," police official Fida Hussain told AFP.

Both Indian and Pakistani fishermen are frequently detained on the charge, as the two countries' borders are not clearly defined in the Arabian Sea and many fishing boats lack the technology needed to be certain of their precise location.

Many are sent to jail before being handed over to the authorities in their homeland.

"The court is likely to send them to jail for at least a year over the violation," Hussain said.

The fishermen often languish in jail even after serving their term, as poor diplomatic ties between the two arch-rivals mean fulfilling official requirements can take a long time.

Shakir Hussain, a senior prison official at Karachi's  Landhi district jail, said more than 400 Indian fishermen were currently detained there.

India and Pakistan have fought three wars since gaining independence from Britain in 1947.