Four Britons have been arrested in China, according to the British embassy, further escalating tensions between the UK and China.

The four Britons were among a group of foreigners arrested in a drugs raid in the city of Xuzhou in the eastern province of Jiangsu on Wednesday, a spokeswoman for the embassy in Beijing said on Friday.

Police in Xuzhou said they had acted on a tip and arrested 19 people whose urine tested positive for drug use. Among them were 16 foreigners, all teachers or students, the police said in a statement.

“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 spokeswoman for the embassy. She said the embassy could not specify whether the arrests of the four Britons were related to the drugs case.

Relations between the UK and China have become strained in recent weeks over mass protests in Hong Kong, a former British colony that was handed back to Chinese control in 1997.

The UK foreign secretary, Jeremy Hunt, has stressed support for “Hong Kong and its freedoms”, calling on Beijing to honour the “one country, two systems” framework that was meant to ensure the territory’s autonomy after the handover.

China’s ambassador to the UK, Liu Xiaoming, has lambasted the UK for “unacceptable interference” and accused Hunt of using “cold war mentality” language when describing ties between China and the UK.

Earlier this month, Liu was summoned to the Foreign Office for a dressing down. UK media, including the Guardian, have been inaccessible in China for several weeks.

What was previously hailed as a golden era of Sino-British ties has also been strained by ongoing uncertainty over whether the UK will allow Huawei to play a role in the building of the UK’s 5G mobile infrastructure.

As Beijing’s ties with other countries fray, observers worry that foreign nationals in China are being targeted and used as leverage. China has sentenced two Canadians to death on drug-trafficking charges this year, as a diplomatic dispute with Ottawa continues over the arrest in Canada of a senior Huawei executive, Meng Wanzhou.

Chinese police also detained a former Canadian diplomat and a Canadian businessman days after Meng’s arrest. The two have since been charged with crimes related to national security.

Amid a protracted trade war with the US, some US businessmen have been blocked from leaving China or held for questioning.

Drug convictions can attract long prison sentences in China, or the death penalty in cases of trafficking. The police in Xuzhou said one of the arrested foreigners had been criminally detained, which means the individual is likely to face formal charges. The rest have been placed under administrative detention, which, under Chinese law, should not last more than 15 days.

Education First, a Swiss-based company that operates a chain of language schools in China, released a statement acknowledging the arrests. It said the company was cooperating with police on the investigation and that employees found to be involved in wrongdoing would be dismissed.

“Education First deeply regrets that some teachers in Xuzhou Center are involved in a drug-related incident during non-working hours,” the statement said.

“We will use this incident as a warning … ensure that every foreign teacher can understand and abide by China’s relevant laws, regulations and policies.”