The United States on Thursday approved a $4 billion sale of state-of-the-art drones to India, offering a new edge to the growing US partner as border tensions simmer with China.

The sale marks a milestone in Indian purchases of American weapons after New Delhi's historic reliance on weapons from Russia.

Indian officials had discussed the drones during a state visit by Prime Minister Narendra Modi last year at the invitation of President Joe Biden, following Indian skirmishes both with China and its historic adversary Pakistan.

After months of discussion, the State Department said it had informed Congress of the sale that includes 31 MQ-9B Sky Guardians, the most advanced among its Predator drones built by General Atomics.

"The proposed sale will improve India's capability to meet current and future threats by enabling unmanned surveillance and reconnaissance patrols in sea lanes of operation," a State Department statement said.

"India has demonstrated a commitment to modernizing its military and will have no difficulty absorbing these articles and services into its armed forces."

The Sea Guardians can monitor the seas as well as submarines and can remain airborne for 35 hours at a time and fire Hellfire missiles and carry around 1,000 pounds (450 kilograms) of bombs.

The sale still needs approval by the US Congress, where most lawmakers favor strong relations with India but several members, especially on the left of Biden's Democratic Party, have criticized Modi's alleged record on human rights.