NEW DELHI, Aug 27 (Reuters) - Indian state refiners have stopped buying crude oil from China-linked companies, three sources said, after New Delhi's recent regulation aimed at restricting imports from countries that it shares a border with.

The new regulation, put in place on July 23, comes after a border clash between India and China that killed 20 Indian soldiers and soured relations between the two neighbours.

Since the new order was issued, state refiners have been inserting a clause in their import tenders on new rules restricting dealings with companies from countries sharing a border with India, the sources said and the tender documents show.

Last week, Indian state refiners decided to stop sending crude import tenders to Chinese trading firm like CNOOC Ltd , Unipec and PetroChina, among others, one of the sources said.

To participate in Indian tenders, the July 23 order makes registration with a department in the federal commerce ministry 'mandatory' for any bidders from nations sharing a border with India.

India shares borders with China, Pakistan, Bangladesh, Myanmar, Nepal and Bhutan, but the government statement did not name any specific country.

State refiners Indian Oil Corp, Bharat Petroleum Corp, Hindustan Petroleum Corp, Mangalore Refinery and Petrochemical did not immediately respond to requests for comment.

CNOOC, PetroChina and Unipec parent Sinopec also did not immediately respond to requests for comment.

(Reporting by Nidhi Verma; additional reporting by Chen Aizhu and Shu Zhang in Singapore and Muyu Xu in Beijing; editing by Florence Tan and Jason Neely)