A British oil executive has been shot dead in front of his wife in Belgium.

Nicholas Mockford, 60, an executive for ExxonMobil, was shot three times as he left an Italian restaurant in a suburb of Brussels. His wife, Mary, was left beaten and covered in blood, cradling her husband and shouting for help.

Witnesses said they saw the couple walk across the street to their Lexus car before shots were fired. Reports suggest two men were spotted running away from the scene, one holding a motorcycle helmet.

The shooting is understood to have happened on 14 October, but the news has only now emerged after Belgian police imposed a reporting blackout.

The Daily Telegraph said police in Belgium were considering all possible motives for the shooting, including an attempted carjacking, although Mockford's car was not stolen.

The Belgian prosecutor's office said a "judicial instruction" from the investigating judge, Martine Quintin, meant they could give no detail about the killing. A spokesman said this was "usual in such a serious murder investigation", the Telegraph reported.

Chief inspector Wim Van Leifferenge said the killing had been reported by Belgian media. He said no one had been arrested for the killing.

A Foreign Office spokesman said: "We can confirm the death of a British national in Brussels on 14 October and we are providing consular assistance."

Mockford is understood to have worked for ExxonMobil since the 1970s and was head of marketing for interim technologies at ExxonMobil Chemicals, Europe, promoting new types of greener fuel. Brought up in Leicestershire, he had moved abroad from Chichester some years ago, living in Belgium and Singapore.

He had been married to his Belgian wife for 15 years and had three grown-up children living in Britain from his first marriage, the Telegraph said.

A family member, who asked not to be named, told the newspaper they thought it was a professional hit. "We are all confused about what has happened. Nick was a genuinely lovely, clean-cut, mild-mannered, family man," the source said. "He was shot so calmly and so quickly, it smacks horribly of a professional hit, but we can't fathom why. He isn't the type to cave in to blackmail and it just doesn't compute."

An ExxonMobil spokesman said: "We are shocked by the tragic death of one of our employees on Sunday 14 October in Brussels. Our thoughts are with his family, friends and colleagues and we are supporting them as best we can at this very difficult time."