U.S. Democratic Senator Joseph Biden says Washington must focus on securing Afghanistan because if it fails, then neighboring Pakistan could be next.

Biden, who is the chairman of the Senate Foreign Relations Committee, made the comment to the Council on Foreign Relations Monday.

He said Afghanistan must never again become a safe haven for al-Qaida, because extremists will - as he put it - "set their sights on the bigger prize to the east" (referring to Pakistan).

Senator Biden also warned that failure in Afghanistan could hurt NATO. Biden said it is time for the alliance to realize it must get fully involved, because if Afghanistan fails, NATO may not be far behind.

Biden just returned from a tour of Afghanistan, Pakistan, India and Turkey with his fellow Democratic Senator John Kerry and Republican Senator Chuck Hagel. The three senators are scheduled to hold a news conference later Tuesday in Washington to discuss their trip.

Some information for this report was provided by AP and Reuters.