Thousands of protesters have gathered outside an air base in eastern India to protest against a joint US-India air force exercise that began on Monday.
The air exercise is the two nations' largest, analysts say
Hundreds of police were deployed at the Kalaikunda base south of Calcutta for the protest by supporters of left-wing parties in the state of West Bengal.
The exercise is the largest between the two air forces and evidence of growing military co-operation, analysts say.
Opponents say the exercise is undermining India's independence.
Police threw a security cordon around the 25 sq km air base as the exercise began with a squadron of US F-16 Falcons being joined by several squadrons of Indian air force fighters.
The BBC's Subir Bhaumik in Calcutta says street protests are also taking place in the city itself, led by senior left-wing leaders.
The leaders have vowed the protests will be peaceful.
Opponents say the exercise compromises Indian independence
West Bengal Chief Minister Buddhadev Bhattacharya said: "We would not have protested if the exercises involved Russian or any other European air force, but we can never accept joint exercises with the US.
"The federal government in Delhi is compromising on India's independent foreign policy by encouraging stronger military relations with the US."
India's Congress-led coalition government depends on left-wing support to stay in power but the two have strong differences, mostly on economic and foreign policy issues.
Defence analysts say the Indian air force is fielding its latest Russian Sukhoi 30 MKI fighters that have never participated in a joint exercise with a foreign air force so far.
The air exercise is scheduled to last until 17 November.
Delhi had close ties with the Soviet Union during the Cold War but ties with the US have steadily improved in recent years.
Earlier this year, India and the US signed a 10-year agreement to strengthen defence ties.
The landmark agreement will help facilitate joint weapons production, co-operation on missile defence and the transfer of technology.
In July the nations agreed to increase co-operation on civilian nuclear energy programmes.