Karzai also acknowledged during a news conference with Pakistani Prime Minister Shaukat Aziz that the relations between the two neighbors have hit a low point, saying the two countries will try to improve them in coming months.
"Mining and fencing the border will not prevent terrorism, but it will divide the two nations," Karzai said of Pakistan's border proposal.
Aziz said the plan, first unveiled last month, is still being considered as part of his country's drive to stop militants from crossing over and launching attacks against Afghan and foreign troops.
"We are exploring many options, including fencing and mining selectively to discourage people from going across the border, people who are not welcomed on the other side," he told reporters after a three-hour meeting with Karzai.
"We are trying to ... identify areas where there may be traffic which is not in line with the security interests of both countries," he said.
But Aziz also called on Afghan authorities to look inside their own country for sources of the growing insurgency that threatens Karzai's government.
Some 4,000 people died in insurgency-related violence in Afghanistan in 2006, the most since the U.S.-led invasion in 2001.
Karzai said closer cooperation is imperative. "If schools continue to get burned in Afghanistan, if teachers continue to get killed, students get discouraged, that means that our meetings are useless," he said.
Relations have soured between Pakistan and Afghanistan, both key U.S. allies in its fight against terrorism. Afghan and Western officials say Taliban and Al Qaeda militants operate from sanctuaries in Pakistan, but Islamabad insists it does all it can to stop them.
Pakistan's plan to fence and mine parts of the mountainous 1,510-mile frontier with Afghanistan was seen as an attempt to fend off criticism. The U.N. has voiced concern over the planned use of land mines.
Aziz also said that he and Karzai agreed to start the repatriation of some 3 million Afghan refugees who remain in Pakistan — although the two leaders did not say when that process would start.
"If Afghanistan and Pakistan have a better relationship ... most of the world will be happy and the people of the two countries will be happy," Aziz said.For more news on Afghanistan, click here.