JOIN USBiden arrived in Kabul Monday to be briefed on efforts made by Afghan security forces to take overall security responsibility of the country from the NATO-led troops by end of 2014.
"It is fair to say we have largely arrested the Taliban momentum here in some very important areas," Biden told a joint press conference with Afghan President Hamid Karzai, referring to recent military gains in the southern provinces of Kandahar and Helmand.
But he cautioned that the success was "fragile and reversible," required strengthening of local security forces and more pressure by neighbouring Pakistan on Taliban fighters residing there.
"It is going to require more pressure on Taliban from Pakistani side of the border than we have been able to observe so far," he said.
Biden is expected to travel to Islamabad Wednesday to discuss cooperation by the Pakistani government in fighting militants in the border region between the two Islamic countries.
In his annual review of war efforts in Afghanistan and Pakistan in December, President Barack Obama said the US would "continue to insist to Pakistani leaders that terrorist safe havens within their borders must be dealt with".
Biden also toured the Kabul Military Training Centre Tuesday, where he was briefed on a program to increase the number of Afghan police and army to around 300,000 by the end of this year.
There are currently around 150,000 army and nearly 120,000 police forces. The US plans to spend $20 billion through 2011 to increase the size and quality of Afghan forces.
Progress in training more Afghan forces is a key to some NATO countries, including the US, to begin the withdrawal of their forces by as early as summer.
Biden said there would be a "condition-based" reduction of forces starting in July, but asserted that the US was prepared to stay in Afghanistan after the complete transition of responsibility to local forces in 2014.
"We are not leaving if you don't want us to leave," he said. Karzai called the talks with Biden "comprehensive" and "satisfactory".