SINGAPORE/LONDON, Dec 21 (Reuters) - Russia's largest producer of liquefied natural gas (LNG), Novatek, has sent force majeure notifications to some of its clients over future LNG supplies from its Arctic LNG 2 project, four industry sources told Reuters on Thursday.

Novatek declined immediate comment on the situation.

The notifications were issued after the United States last month imposed sanctions on Arctic LNG 2, which is due to start production before the end of this year or in early 2024.

The project is a key element of Russia's drive to increase its market share on the global LNG market to a fifth by 2030 - from around 8% now. The first LNG tankers from the project were expected to set sail in the first quarter of next year.

One of the sources said that clients who had contracted to buy the LNG, such as Chinese companies Shenergy Group and Zheijang Energy, as well as Spain's Repsol, had received force majeure notifications.

Repsol did not immediately reply to a request for comment.

Shenergy Group and Zheijang Energy were not immediately available for comment outside of business hours.

A seller of goods or services may declare force majeure in the event that they cannot supply them due to circumstances beyond their control. In such a case, they must notify the other party and offer an explanation. (Reporting by Chen Aizhu and Marwa Rashad; additional reporting by Emily Chow; Editing by Andrew Osborn)