CHAMAN, Pakistan (AP) - The first truck carrying supplies to American and NATO troops in Afghanistan has crossed the Pakistani border after a seven-month long closure of the supply routes by Pakistan ended earlier this week. In the port city of Karachi, truck drivers were preparing their vehicles for the trip. Thousands of trucks and tankers have been stuck at ports in Karachi waiting for the transit ban to be lifted as diplomatic wrangling dragged on. The chairman of Port Qasim, Mohammad Shafi, said Thursday that more than 2,500 NATO containers and vehicles have been held at the facility since the blockade began. Getting them back on the road will take time, Shafi said, due to paperwork and customs clearance procedures. The journey is a perilous one, as the Taliban and other militant groups have threatened to attack supply vehicles in Pakistani territory. Before the closure, hundreds of supply trucks, which travel in convoys, were targeted in different areas of the country. U.S. officials had expected the first trucks carrying NATO supplies to begin crossing into Afghanistan on Wednesday, but bureaucratic delays held that up. The reopening could save the U.S. hundreds of millions of dollars, since Pakistan's blockade forced Washington to rely more heavily on a longer, costlier route that leads into Afghanistan through Central Asia. Pakistan is also expected to gain financially, since the U.S. intends to free up $1.1 billion in military aid that has been frozen for the past year. But the deal carries risks for both governments. Pakistan is already facing domestic backlash, given rampant anti-American sentiment in the country and the government's failure to force the U.S. to stop drone strikes targeting militants and accede to other demands made by parliament. President Barack Obama, in the midst of a re-election battle, faces criticism from Republicans who are angry his administration apologized to a country allegedly giving safe haven to militants attacking American troops in Afghanistan.