CHANDIGARH, India (Reuters) - Troops and police patrolled towns, highways and train stations to enforce a curfew in India's northern state of Punjab on Tuesday after two people were killed in riots sparked by the killing of a Sikh preacher in Austria.

More than 8,000 railway passengers remained stranded in the neighboring state of Jammu and Kashmir after the violence brought some railway services to a standstill.

Most shops in areas hit by Monday's protests remained closed for a second day, but authorities began to slowly relax the curfew in some areas.

"The curfew has been relaxed from 10 a.m. to 2 p.m. and the time could be extended if there is no violence," senior state police official Vikas Garg said.

Thousands of dalits, or "untouchables," torched trains, cars and shops on Monday to protest against the killing of a leader of a religious sect in an attack on a temple in Vienna, prompting Indian Prime Minister Manmohan Singh to appeal for calm.

The preacher who died was from the Dera Sach Khand, which has a large dalit following in India of lower caste Sikhs and Hindus.

At least 16 people were also hurt in Vienna on Sunday when six armed men attacked the temple.

Austrian police said they did not know yet about the motives for the attack.

Sikhism officially rejects caste but social hierarchies still prevail. Dera Sach Khand has gained many followers from the dalit community in Punjab and is opposed by many mainstream Sikhs.

The riots caused U.S. retailer Wal-Mart Stores Inc to postpone the launch of its first cash-and-carry store in India, which was scheduled to open in Punjab on Tuesday.

(Additional reporting by Ashok Pahalwan in Jammu; Editing by Matthias Williams and Alex Richardson)