"There is some way to go in discussions between GM and PSA but I was reassured by GM's intention, communicated to me, to build on the success of these operations rather than rationalise them," the minister said in a statement.
GM had recently made "significant investments" at its Ellesmere Port and Luton plants, he said.
Clark spoke following a meeting with US auto giant GM's president Dan Ammann in London, two days after it emerged that PSA, which owns the Peugeot, Citroen and DS brands, was in talks to take over GM's European brands Opel and Vauxhall.
The economy minister will travel to Paris for separate meetings tomorrow with French Industry minister Christophe Sirugue and board members of PSA Group, a spokeswoman for Clark told AFP.
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The potential purchase of Vauxhall has spooked trade unions as the carmaker employs about 35,000 people in Britain.
Len McCluskey, the general secretary of Unite, Britain's largest trade union, said yesterday following a meeting with Clark that his organisation would "not accept any job losses or plant closures".
Japanese carmaker Nissan said in October that it would continue to invest in its Sunderland plant after securing guarantees about Brexit from the British government.