Dozens of US President Joe Biden's fellow Democrats urged him on Tuesday to raise human rights issues with Indian Prime Minister Narendra Modi during his visit to Washington this week, according to a letter sent to Biden.

Modi left for Washington on Tuesday for a visit projected as a milestone in ties between the two countries.

The US lawmakers said they were concerned about religious intolerance, press freedoms, internet access and the targeting of civil society groups.

"We do not endorse any particular Indian leader or political party — that is the decision of the people of India — but we do stand in support of the important principles that should be a core part of American foreign policy," said the letter, led by Senator Chris Van Hollen and Representative Pramila Jayapal.

A total of 75 Democratic senators and members of the House of Representatives signed the letter, sent to the White House on Tuesday and first reported by Reuters.

"And we ask that, during your meeting with Prime Minister Modi, you discuss the full range of issues important to a successful, strong, and long-term relationship between our two great countries," the letter said.

Modi has been to the United States five times since becoming prime minister in 2014, but the trip will be his first with the full diplomatic status of a state visit, despite concerns over what is seen as a deteriorating human rights situation under his Hindu nationalist Bharatiya Janata Party.

Washington hopes for closer ties with the world's largest democracy, which it sees as a counterweight to China, but rights advocates worry that geopolitics will overshadow human rights issues. Several U.S. rights groups plan protests during Modi's visit.

The State Department's annual report on human rights practices released in March listed "significant human rights issues" and abuses in India.

'Friends can and should discuss their differences'

Modi will address a joint meeting of the House and Senate on Thursday, one of the highest honors Washington affords to foreign dignitaries.

"A series of independent, credible reports reflect troubling signs in India toward the shrinking of political space, the rise of religious intolerance, the targeting of civil society organizations and journalists, and growing restrictions on press freedoms and internet access," the lawmakers said in the letter.

They said they joined Biden in welcoming Modi to the United States, and want a "close and warm relationship" between the people of the two countries, saying that friendship should be based on shared values and "friends can and should discuss their differences in an honest and forthright way."

"That is why we respectfully request that — in addition to the many areas of shared interests between India and the US — you also raise directly with Prime Minister Modi areas of concern," the letter said.

Speaking to reporters before Modi arrived in Washington, White House national security spokesperson John Kirby declined comment on whether Biden would raise the issue, but that it is "commonplace" for Biden to raise concerns about human rights.