United States President Barack Obama and Russian President Dmitry Medvedev announced Monday that they had signed a preliminary agreement to reduce their nations' nuclear stockpiles. The two countries will cut back on their nuclear arsenals by up to 30 percent.

The reduction would leave both America and Russia with no more than 1,675 nuclear warheads and 1,000 long-range missiles that could deliver nuclear bombs. However, the two sides have not yet reached a final agreement on what to consider a warhead.

Both leaders linked their agreement to concerns over nuclear proliferation worldwide. “We must lead by example, and that's what we are doing here today,” Obama told reporters in the Kremlin.

"We are seeing a pace of proliferation that we have not seen in some time,” Obama said. He expressed concern over nuclear programs in Iran and North Korea in particular.

Medvedev said Russia and the U.S. share a “common, joint responsibility” to monitor nuclear programs in North Korea and the Middle East.

The two also touted the reduction deal as a step towards improved Russia-U.S. Relations. The countries have suffered a “drift” in recent years, said Obama, who pledged to work for closer ties.

America and Russia still disagree on key issues, including the status of Georgia and the proposed construction of a missile defense system based in eastern Europe, Obama said. He emphasized that the proposed missile shield would be built not as a defense against Russia, but against “an entirely different threat.”