MOSCOW (AP) — Russia has suspended an agreement with the United States on research cooperation in the nuclear and energy sectors, the latest move underlining worsening tensions between Washington and Moscow.

A suspension decree signed by Prime Minister Dmitry Medvedev was posted Wednesday on the government website, which said the decree was a "countermeasure" to U.S. sanctions imposed over Russia's role in the Ukraine conflict.

The impact of the move is likely to be less serious than Russia's suspension Monday of an agreement on disposal of weapons-grade plutonium. That agreement had been seen as a symbol of US-Russian rapprochement.

The strain in Moscow-Washington relations over Ukraine has intensified in recent weeks amid the collapse of a cease-fire in Syria and the Syrian army's assault on the city of Aleppo under cover of Russian warplanes.

State Department spokesman Mark Toner said the U.S. has not received notification of the suspension, but "would regret the Russian decision to unilaterally suspend cooperation on what we believe is a very important issue that's in the interests of both our countries."