Islamabad, Pakistan ? Secretary of State Condoleezza Rice sought Tuesday to heal a rift between Pakistan and Afghanistan, two Muslim allies of the United States, but tensions spilled over during a news conference in which Pakistani Foreign Minister Khursheed Kasuri angrily accused the Afghan government of making false charges.

Rice smiled tightly during Kasuri’s five-minute emotional outburst, which was prompted by a question about Afghan claims that Pakistan is allowing its largely lawless border areas to shelter insurgents who are mounting their biggest offensive in Afghanistan since the Taliban was ousted in 2001.

With close to 10,000 international troops conducting sweeps in rugged southern Afghanistan, Rice’s trip here was organized on short notice in an effort to end feuding that many analysts say is undermining efforts to stabilize the government of President Hamid Karzai.

Kasuri said Pakistan would add 10,000 troops to the 80,000 now operating in areas bordering Afghanistan. He noted that already “we have 650-plus martyred soldiers.” Officials offered few other details of the content of the talks.

Rice plans to fly today to Kabul to meet with Karzai, who is facing mounting international criticism over his performance. As she traveled to Islamabad on Monday, Rice hailed Karzai as “an extraordinary leader” and said the United States would “back him fully.”

Rice’s visit comes as Karzai is straining to hold his country together, but is losing popular support because of increasing violence, corruption, drug trafficking and an inability to demonstrate tangible progress since the fall of the Taliban. A failure of the Karzai government would undermine Bush administration claims that Afghanistan has become a symbol of rising freedom and democracy in the world.

It is a sensitive time in Pakistan too. With elections scheduled for next year, there are signs that Gen. Pervez Musharraf – whose military efforts in the border areas are not popular in Pakistan – is maneuvering to extend his presidential term.