Indian and Pakistani troops traded cross-border fire Sunday, officials said, the latest in a series of clashes that began earlier this month and have claimed at least 20 civilian lives.

No one was injured in the latest incident, which according to a Pakistani army statement began when Indian troops resorted to “unprovoked” fire across the border that separates Indian-held Kashmir and Pakistan’s Punjab province.

Pakistani soldiers at the Kashmir border with India

Each country holds part of the Himalayan territory but claims it in full. The two nations have fought two full-scale wars over Kashmir, though tensions have eased since the signing of a 2003 ceasefire.

It is still unclear what precipitated the recent upsurge in unrest, which began on October 6 during the Islamic festival of Eid ul-Adha and has forced thousands of residents on both sides to flee their homes.

Pakistan’s most senior foreign affairs official Sartaj Aziz meanwhile had a phone conversation with UN Secretary-General Ban Ki-moon, officials said. He told Ban that Islamabad “was fully united and determined to thwart any aggression”, according to a statement released by his office.

Aziz also called on the UN to implement its 1947 resolution calling for a referendum in Kashmir to determine its fate and restore peace to the region — a resolution India has long rejected.