"NATO Allies have expressed serious concerns over the conduct of the presidential election in Belarus," Stoltenberg said, in a statement from the alliance's Brussels headquarters.

"NATO condemns violence against peaceful protestors. Fundamental rights must be respected, including freedom of speech and the right to peaceful protest," he said.

Long-serving Belarus strongman Alexander Lukashenko was declared the winner of Sunday's presidential poll by a huge margin, but protesters took to the streets to denounce what they see as fraud.

Several European capitals have expressed concern over the results.