A top U.N. human rights officer said Wednesday that Pakistan's plan to mine parts of its border with Afghanistan would only add to civilian casualties in a region already littered with unexploded ordnance.

Pakistan said Tuesday it would plant land mines and build a fence on parts of its 1,500-mile frontier with Afghanistan to fend off criticism it does too little to stop Taliban and Al Qaeda guerrillas from crossing the border.

"From a human rights perspective, we would be concerned about any mining, including this," said Richard Bennett, the U.N.'s chief human rights officer in Afghanistan. "Human rights advocates are solidly opposed globally to the use of land mines. The U.N. is opposed to the use of mines."

Afghanistan is one of the world's most mine-affected countries, with thousands of civilian deaths and maimings in the past 25 years of war. The frontier region is inhabited on both sides by Pashtun tribespeople who travel freely across the border.

Taliban-led insurgents have stepped up attacks in Afghanistan over the past year, triggering the worst violence since U.S.-led forces ousted the hardline regime five years ago and threatening the shaky rule of Hamid Karzai, the nation's first popularly elected president.

Aleem Siddique, a spokesman for the U.N. assistance mission to Afghanistan, there needs to be better coordination between Pakistan and Afghanistan to fight the insurgency.

"It's difficult to see what value laying fresh mines could bring to the people of either country," he said.

Relations have been souring between the neighbors, which are key U.S. allies in its fight against terrorism. Afghan and Western officials contend militants operate from sanctuaries in Pakistan, but Islamabad insists it does all it can to stop them.

A spokesman for the NATO-led security mission in Afghanistan said the Pakistani mining plan should be discussed by Afghan, Pakistani and NATO commanders.

"We obviously applaud any statement about further efforts to improve border security, but the methodology should be discussed in the tripartite council," said Mark Laity, senior civil representative spokesman for the International Security Assistance Force.

Afghanistan quickly objected to the idea of a fence along the rugged border, whose demarcation is disputed by the two nations. But Pakistani Foreign Secretary Riaz Mohammed Khan said his country would be acting on its own territory and did not need Afghan consent.

Khan told reporters Pakistan also will send unspecified military reinforcements to the frontier, joining about 80,000 soldiers already in the country's northwestern tribal regions.

He did not say when the mining and fence work would start.