Vice President of United States Joe Biden has arrived in Pakistan to strengthen a vital but often troubled alliance in the fight against extremism.

Washington is committed to giving Pakistan $7.5 billion in aid over the next five years. It is also asking Islamabad to step up military efforts against militants in northwest.

Biden is expected to discuss both elements of U.S. strategy with Pakistani political and military leaders during his brief trip on Wednesday.

His trip was not disclosed ahead of time for security reasons, as is common in Pakistan.