India and Pakistan have begun two days of talks on a long-running border demarcation dispute.
The talks in the Pakistani city of Rawalpindi are focusing on Sir Creek, a narrow strip of marsh land separating India's western border from Pakistan.
The dispute over Sir Creek has hampered the search for oil and gas and led to hundreds of fishermen being arrested.
Both sides freed dozens of the other's nationals from their jails as talks got underway. Peace moves began in 2004.
Pakistan freed 70 Indian prisoners, 50 of them fishermen, from jails in Karachi and Lahore, while India repatriated 57 Pakistanis at the Wagah border crossing.
The two sides routinely arrest each other's fishermen for alleged border violations.
The fishermen say they are often unsure whose waters they are in because of the dispute.
In May, the two sides decided to do a joint survey of Sir Creek and adjoining areas to obtain information which would allow for better decisions to be made.
"The delegation of the two countries will deliberate and work out a mechanism for undertaking a joint survey in Sir Creek," a Pakistani defence ministry release said.
It said military officials from the two countries will discuss modalities for conducting the survey during the talks in the Pakistani city of Rawalpindi.
Sir Creek lies between the Indian state of Gujarat and the southern Pakistani province of Sindh.
Much of the land is either marsh or desert that neither side sees as being militarily important. It is also sparsely populated.
But this inhospitable terrain - famous on the Indian side for its high quantities of salt - was the scene of heavy fighting between India and Pakistan in 1965.
India says the boundary should be in the middle of the 100-km (60-mile) estuary. Pakistan says the border should lie on the south-east bank.