DHAKA, Bangladesh

In a letter to Bangladeshi Prime Minister Sheikh Hasina, 12 US senators urged an end to the "persistent harassment" of Nobel laureate Muhammad Yunus, who is battling a string of graft cases.

Earlier this month, a court handed down a six-month prison sentence to Yunus and three of his colleagues for allegedly violating the country’s labor laws. They, however, got bail as the verdict was appealed in a higher court.

“We write urging you to end the persistent harassment of Nobel Peace Prize laureate Professor Muhammad Yunus -- and the pattern of abusing laws and the justice system to target critics of the government more broadly,” the letter read.

The letter also referred to the UN High Commissioner for Human Rights and other human rights organizations who noted irregularities in proceedings against Yunus.

"Yunus’s pioneering work on microfinance offered greater economic promise for many Bangladeshis and millions of impoverished people around the world. Such efforts should not be undermined over ongoing political vendettas, especially in a democratic nation of laws," it continued.

"The United States values its longstanding relationship with Bangladesh, which includes close bilateral and multilateral coordination on numerous common interests," said the letter, adding that “ending the harassment of Professor Yunus, and others exercising their freedom of speech to criticize the government, will help continue this important relationship.”

Reacting to the senators' call, Bangladeshi Foreign Minister Hasan Mahmud said that the government has “nothing to do with the Yunus case."

Talking to reporters at a news conferences at his office in Dhaka, he said the court is handling the matter.

The 83-year-old chairman of Grameen Telecom, a nonprofit company, has been embroiled in a longstanding row with the government. He is battling at least 168 cases, including alleged tax evasion and misappropriation of profits.

Earlier, 40 world leaders and Nobel laureates had written a letter to Prime Minister Hasina over her government’s treatment of Yunus.

The government, however, termed the letter part of a conspiracy.

Yunus, a Bangladeshi social entrepreneur, banker, economist and civil society leader, was awarded the Nobel Peace Prize in 2006 for founding Grameen Bank and pioneering the concepts of microcredit and microfinance. The loans are given to entrepreneurs who are too poor to qualify for traditional bank loans.