International Monetary Fund says, Pakistan is facing serious economic challenges and it needs to carry out a set of comprehensive economic reforms. Disclosing this in Washington, the IMF Deputy Managing Director and Acting Chair Nemat Shafik said, overall vulnerabilities and crisis risks are high with sub par growth and unsustainable fiscal and balance of payments positions.The comments came hours after approval of a financial assistance of 6.7 billion dollar to prevent the country from a brink of economic collapse. She said, tax administration overhaul is also required and provinces should contribute fully to the adjustment effort.