SHANGHAI (REUTERS) - China is investigating two Canadian nationals for suspected theft of state secrets involving military and national defence research, the official Xinhua news agency said on Tuesday.

Xinhua identified the two Canadians as Kevin Garratt and Julia Dawn Garratt, but did not say whether they had been detained. It said the State Security Bureau of Dandong City, in north-east China's Liaoning Province, was investigating the case.

China's Foreign Ministry said on Tuesday that the two Canadians are suspected of stealing military information and threatening the country's national security,

The Canadian embassy in Beijing had been notified and the suspects' rights were being "guaranteed", the ministry said in a short statement sent to Reuters.

Canadian newspaper The Globe & Mail said the Vancouver couple had been living in China since 1984 and opened a coffee shop called Peter's Coffee House in Dandong in 2008. The couple previously worked as teachers in southern China.

The western-style coffee shop had a view of traffic flowing across the China-North Korea border, said the newspaper, adding the couple had a side business helping holidaymakers plan tours to North Korea across the Yalu River.

It said the immediate whereabouts of the Garratts was unknown and calls to their coffee shop went unanswered.

The investigation comes a week after Canada took the unusual step of singling out Chinese hackers for attacking a key computer network and lodged a protest with Beijing.