More than 50 prominent political prisoners in Iran have written to Barack Obama, asking him to end "crippling" sanctions and seize "the last chance" for dialogue with Tehran.

In a letter published by the Guardian, leading opposition figures, who with only a few exceptions are currently behind bars in some of the Islamic republic's most notorious prisons, urged Obama to take the opportunity created by the election of Hassan Rouhani, as Iran's new and moderate president, to seek detente between the two countries.

The signatories were also critical of the US sanctions on Iran, which they said had had "devastating effects" on the lives of ordinary people.

"We believe the time has come for our two countries to turn a page and start a new era of mutual understanding," reads the letter, which is signed by 55 former officials, activists, journalists and dissidents.

Hopes of a rapprochement have increased in recent days as both countries sent positive signals after Rouhani's inauguration on Sunday. The White House issued a statement that said Tehran would find "a willing partner in the United States" should it choose to engage. Rouhani said in his first press conference that his government would be open to direct talks with the US should Washington show goodwill and engage in "practical steps".

Rouhani said the contrast between the White House statement and the new sanctions bill passed by the House of Representatives showed inconsistency between US words and actions in its stance on Iran. Rouhani attacked the US sanctions, saying there were designed to pressure ordinary people.

In their letter, the political prisoners made clear that they agreed with Rouhani on sanctions, even though they are in most cases serving lengthy prison terms for criticising the government he represents.

"All Iranian people, including the families of political prisoners and especially the low income groups, are suffering under the burden of rampant inflation and shortages of medical supplies and other basic necessities of life," the letter reads. "The sanctions have now turned into a collective punishment imposed on the Iranian people as a whole, not the government only. The national economy has shrunk over the past couple of years and the strength of Iran as a nation-state is being reduced."

The signatories described Rouhani as "a politician known to be a firm believer in dialogue and constructive engagement in international relations" who also enjoys "a solid base of support".

"In our view, the tenure of this government may be the last chance to bring this conflict to a reasonable and mutually acceptable resolution."

The letter warned, however, that "continuing with the pressure track of these past years will strengthen the belief in a significant part of the Iranian public that the United States is not genuinely interested in resolving the conflict".