The biggest East-West prisoner exchange since the Cold War last week was hailed as a triumph by both Washington and Moscow. But it left the family and friends of a jailed Nobel Prize winner and other imprisoned opponents of President Aleskandr G. Lukashenko, the longtime dictator of Belarus, puzzled and bitterly disappointed.

Belarus was involved in the swap, releasing a German national who had been sentenced to death, but it freed none of its nearly 1,400 inmates classified as political prisoners by Viasna, a human rights organization, as Russia did.

“We are very saddened that not a single Belarusian was released,” said Alena Masliukova, an activist with Viasna. She added that “Belarus has more political prisoners than Russia: 1,400 in Belarus compared to 700 in Russia,” but unlike Russia has faced little sustained pressure to set its prisoners free.

That may be because Belarus, which has fewer than 10 million people and has been ruled since 1994 by Mr. Lukashenko, is widely viewed as an eccentric Russian puppet state and, despite a sustained reign of terror, commands little attention in its own right.

But the absence of Belarusian prisoners from last week’s sprawling exchange has raised questions about why opponents of Mr. Lukashenko abroad, led by Svetlana Tikhanovskaya, the self-styled national leader of Belarus, have failed to make the release of prisoners a priority for the United States and other Western governments.

That stands in stark contrast to Russia’s opposition movement in exile, which has campaigned vigorously to have Russian dissidents freed.