U.S. Vice President Joe Biden has arrived in Kabul to pay a suprise visit to Afghanistan on Monday night.

When asked about his suprise visit, the Afghan government and the presidential palace refused to make any comments due to security reasons.

Right now Kabul is on high security alert, it is heared that several helicopters flying and hovering across the air.

Joe Biden is scheduled to meet Afghan President Hamid Karzai. Some media reported that the aim of Biden's visit is to make assessment of the progress of the handling of security to Afghan security forces.

The United States will begin the withdrawal of its combat forces this July, but a lot of doubts remain due to the weakness of the Afghan National Amry and the Afghan police.

According to the presidential palace, there will be a press conference on Tuesday, but it refused to give further details. This is the second vist of Joe Biden to Afghanistan since January 2009. On Dec. 3, 2010, U.S. President Barack Obama arrived in the Bagram Air Base, 50 kilometers north of Afghanistan' s capital Kabul, paying a surprise visit to Afghanistan.