Former Jammu and Kashmir Chief Ministers had been put under house arrest just ahead of the announcement
After the government's move to end Jammu and Kashmir's special status under Article 370 of the constitution, Washington on Monday urged respect for rights and called for the maintenance of peace along the Line of Control in Kashmir.
"We are concerned about reports of detentions and urge respect for individual rights and discussion with those in affected communities," State Department spokeswoman Morgan Ortagus said in a statement.
Just ahead of the announcement, former Chief Ministers and mainstream leaders of the state had been put under house arrest.
"We call on all parties to maintain peace and stability along the Line of Control", Ortagus said.
Home Minister Amit Shah rushed through a presidential order to scrap from the constitution special status for Jammu and Kashmir. It also moved a bill proposing the state be divided into two union territories.
Ortagus said the US is "closely following" events in Jammu and Kashmir, but noted that India has described its actions as "strictly an internal matter."
US President Donald Trump last month claimed, during a meeting with Pakistani Prime Minister Imran Khan, that PM Modi had asked President Trump to help mediate on Kashmir.
While Pakistan has often sought third-party mediation in various international forums, including the United Nations, India has maintained that the issue can only be resolved bilaterally.