Image copyright Getty Images Image caption (File photo) They were arrested in the city of Xuzhou in Jiangsu province

Four Britons have been arrested in China's Jiangsu province over drug-related offences.

They are among 16 foreigners - seven teachers and nine students - who were detained last week after testing positive for drug use.

At least some of those being held are from an international language school, Education First.

Police did not specify the type of drugs involved and it is not clear where the other foreigners are from.

There are extremely severe penalties for drug offences in China.

"We are in contact with the Chinese authorities following the arrest of four British people in Jiangsu province, and are providing consular assistance," said the British embassy in Beijing.

On Tuesday, the Xuzhou Public Security Bureau, located in Jiangsu province, posted a statement on Chinese social media site Weibo saying police had successfully cracked a drug-related case.

It said 19 people had been arrested, including 16 foreigners.

According to police, 18 people had been placed under administrative detention, which carries a maximum detention period of 15 days. One person was placed in criminal detention - a procedure that usually leads to a formal arrest and an indictment.

Police did not name the school involved, but state news agency Xinhua later reported that some of the teachers were from the Switzerland-based Education First (EF) Centre.

The EF centre told Xinhua it had a "zero tolerance" policy towards drugs, adding that it was deeply regretful that some of its teachers were involved.

It said the drug-related incident had taken place during "non-work" hours.

EF first entered China in 1998 and has around 2,000 English teachers now based in the country.