North Korea could increase its nuclear arsenal from at least 10 weapons today to between 20 and 100 weapons in five years, U.S. researchers said Tuesday, as the Obama administration vowed to work with U.S. allies to pressure Pyongyang to denuclearize.

The forecast of the secretive Asian nation's nuclear stockpile is based on projections made by American experts on weapons technology and the experience of nuclear programs of countries such as Israel, Pakistan, India and China. The findings were presented by the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies in Washington.

It comes as the U.S. and South Korea begin annual military drills that have angered North Korea, and as U.S. lawmakers push legislation that would tighten sanctions intended to restrict leader Kim Jong Un's access to the international banking system. Aid-for-disarmament negotiations have stalled since 2008, and the North has since conducted two nuclear tests, fired a rocket into space and unveiled a long-range, road-mobile missile, deepening concern in Washington over its capabilities.

"The United States remains committed to the peaceful denuclearization of the Korean Peninsula and will continue - in close consultation with our allies — to bring pressure to bear on North Korea in support of that goal," Secretary of State John Kerry said in congressional testimony Tuesday.

But North Korea struggles for attention in a crowded U.S. foreign policy agenda. During two Senate hearings, Kerry was peppered with questions about Ukraine, the fight against the Islamic State group and nuclear negotiations with Iran, but none on North Korea.

The U.S.-Korea Institute concluded that North Korea has made important progress in its weapons programs in the past five years, and those programs "appear posed for significant expansion over the next five years, presenting a serious challenge to the United States, Northeast Asia and the international community."

In its analysis, provided to The Associated Press ahead of publication on its website, 38 North, the institute estimated that North Korea currently has between 10 and 16 nuclear weapons, some based on plutonium, others on uranium. It said U.S. experts meeting in October came up with various scenarios on how that stockpile could grow by 2020.

Under the "minimal growth" scenario, the North would have 20 weapons with yields of about 10 kilotons. A kiloton is equivalent to the destructive impact of 1,000 kilograms of TNT. The U.S. bomb dropped on Hiroshima, Japan, in 1945 was estimated to have a yield of 15 kilotons.

Under the "rapid growth" scenario, in which the North accelerates nuclear production and makes significant advances in weapons designs, it would have 100 weapons with average yield of 20 kilotons, and some of 50 kilotons.

Despite orthodox opinion that North Korea has yet to miniaturize a nuclear device that could fit on a missile that could target America, the institute concludes the North already has plutonium-based weapons small enough to mount on medium-range and intercontinental-range missiles.