European and US negotiators have been in talks for more than a year to create the world's biggest free-trade and investment agreement, the proposed Transatlantic Trade and Investment Partnership (TTIP).
"The challenges facing Europe today are serious and TTIP is a serious response to those challenges," Malmstroem said in a European parliament debate.
The ambitious pact, which would harmonise the world's two biggest economies, has drawn sharp criticism by labour unions and activists and confidence has dimmed that a deal can emerge.
Criticism has focused on the so-called investor-state dispute settlement, or ISDS, which would allow firms to sue national governments if they feel that local laws -- such as health and safety regulations -- violate the trade deal and threaten their investments.
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Briefing parliament yesterday after his return from the G20, British Prime Minister David Cameron brushed off the ISDS controversy.
"We have had these in every single trade deal that we have ever signed," Cameron said.
Malmstroem said the Commission negotiators would remain vigilant when it came to protecting a government's ability to protect consumers and indicated that the reach of any ISDS would be limited.
ISDS must be "limited to the most obvious cases that have threatened investment," she said.
Also at the debate, Michael Punke, the US ambassador to the World Trade Organization, said that thousands of versions of ISDS existed in trade deals around the world.
"I think ISDS is an enormously complex topic that gets oversimplified," said Punke.
Malmstroem, who took office on November 1, meets with US trade representative Michael Froman in Brussels on Friday.