, Feb. 5 (Xinhua) -- UN Secretary-General Antonio Guterres on Monday congratulated the and on successfully reducing their strategic nuclear forces to the level required by the new START treaty.

"The secretary-general stresses that at a time when global anxieties about nuclear weapons are higher than at any time since the Cold War, efforts in nuclear disarmament, non-proliferation and arms control are more vital than ever," said Guterres' spokesman Stephane Dujarric.

"These endeavors can play significant roles in building trust and confidence, and preventing, mitigating and resolving conflicts."

The UN chief called on the United States and Russia to engage in the necessary dialogue that will lead to further arsenal reductions and to continue to display "the historic leadership across the multilateral disarmament agenda that has proven so valuable to our collective security," said Dujarric in a statement.

New START, officially called Measures for the Further Reduction and Limitation of Strategic Offensive Arms, reduces deployed nuclear weapons to 700 delivery vehicles and 1,550 warheads. The treaty, signed in April 2010 in Prague, the Czech Republic, entered into force in February 2011. It is expected to last at least until 2021.