Chinese officials have arrested and detained a Christian couple from Canada on grounds of the suspected theft of intelligence information.

The Foreign Ministry confirmed yesterday that Kevin and Julia Dawn Garratt, who have lived in China since 1984, are suspected of "collecting and stealing intelligence materials related to Chinese military targets and important Chinese national defence scientific research programmes, and engaging in activities that endanger China's national security."

The couple were arrested in the city of Dandong, where they run a coffee shop, on Monday evening, and their three grown-up children have not heard from them since.

Dandong is China's largest border city, with North Korea accessible via the "Friendship Bridge" over the Yalu River. According to Reuters, it is home to a Chinese air force base.

The Garratts are said to be close to the missionary community in the area, and the Guardian reports that in a talk to a church in British Columbia last year, Kevin – a Pentecostal pastor – said he and his wife "are trying to reach North Korea with love and practical assistance" after receiving a vision from God.

"God said: 'Go to Dandong and I will meet you there.' And he said: 'Start a coffee house'...We're China based, we're North Korea focussed, but we're Jesus centred," Kevin declared.

He also reportedly shared of being involved in delivering aid to North Korea, and of running a "training house" for North Koreans who now live over the border in China.

Their eldest son, Simeon Garratt, has dismissed the allegations against his parents as "wildly absurd".

"I know for a fact it's not true," he added.

China has apparently been tightening its security in border regions, and foreigners are said to be facing close scrutiny. The government has also been cracking down on Christians across the country, particularly in Zhejiang province – almost 2,000 miles south of Dandong – where at least 360 churches have been completely or partially demolished.

Though the couple are funded by a church back in Canada, Simeon told CTV News Channel it is unlikely that the Garratt's Christian faith has anything to do with their arrest. "They have always had a passion for helping people...It seems crazy that something so good can turn into some sort of spy case," he said.

"It's never been a secret that they've been Christian. There's nothing that has happened in the last week or so that would have changed the situation."

The Garratt's youngest son Peter, after whom their cafe is named and who also lives in Dandong, told Canada's CBC News that he himself was questioned and released, and was asked to bring clothes and toiletries to the local State Security Bureau in the city. He assumes that this is where his parents are being held, though he wasn't allowed to speak to them.

"I have no idea where they [the accusations] are coming from or how it even came about," he told the news service.

The spokesperson for the Chinese Embassy in Canada, Yang Yundong, has released a statement insisting that "various rights of the couple have been fully guaranteed".

"We believe there is no need to over interpret this case. If we have further information, we will release it timely," the statement concluded.