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Unilever, which owns some of the UK's most famous household brands, has strongly rejected a takeover bid from US food giant Kraft Heinz.

The maker of Marmite and PG Tips said it saw "no merit, either financial or strategic" in Kraft's offer, worth about $143bn (£115bn).

But Kraft, which makes Heinz ketchup, indicated it would continue working on a deal for the Anglo-Dutch firm.

The deal would be one of the biggest in corporate history.

It would combine Unilever's dozens of household names, which also includes Ben & Jerry's ice cream, Dove soap, and Hellmann's mayonnaise, with Kraft's own wide range, such as Philadelphia cheese and Heinz baked beans.

Shares in both companies rose sharply on Friday, as investors welcomed the possible creation of such a powerful firm.

But a deal could also raise concerns about job cuts and would probably be examined by competition regulators, analysts said.

Unilever: Profile of a consumer giant

Unilever, which has 7,500 employees in the UK, said Kraft's offer "fundamentally undervalued" the company. "Unilever does not see the basis for any further discussions," it added.

Kraft, which is part-owned by US billionaire Warren Buffett, said it had made "a comprehensive proposal" and looked "forward to working to reach agreement on the terms of a transaction".

The US food company attracted political scrutiny when it bought Cadbury in 2010, although it later spun the UK chocolate maker off into another company.

'Flex muscles'

The UK government has no "legal powers" to block a Kraft-Unilever deal, but competition regulators would need to investigate it, said former Business Secretary Sir Vince Cable.

Analysis - When does 'no' mean 'no'?

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By Jonty Bloom, BBC business correspondent

Takeovers are like those strange mating rituals you see on Planet Earth narrated by David Attenborough.

Kraft Heinz has approached Unilever about getting together and making an even bigger business with a huge family of brands.

Unilever has spurned the offer and is looking aloof, saying not only the proposal was too cheap but also that it "sees no merit, either financial or strategic".

Quite a slap in the face you might think but faint heart ne'er won fair hand. If Kraft Heinz offered a lot more money it might look a bit more attractive to Unilever.

Although whether the competition and takeover authorities would bless the union is another matter.

It would create a behemoth that could dominate many consumer sectors from food to soap and might stifle competition; many societies have rules against that kind of relationship.

With so many brands, Kraft-Unilever would be in a stronger position to raise prices, said Neil Wilson, an analyst at London broker ETX Capital.

"The combined entity would have a huge brand footprint and be able to flex bargain muscles even more with supermarkets," Mr Wilson said.

"It could come up against a number of hurdles as it would create a giant in the sector. EU regulators in particular could be against it," Mr Wilson said.

Unilever clashed with UK supermarket Tesco in October over its attempts to raise prices to compensate for the steep drop in the value of the pound.

The consumer goods giant has over a dozen sites across the UK, including three major plants in Liverpool, Norwich and Gloucester.

A UK government spokesman said: "This is clearly an important potential deal for a major company in the UK and its workforce. We continue to monitor the situation closely."

'Test the water'

If the deal went through, it would be the second biggest ever, behind Vodafone's $183bn takeover of Germany's Mannesmann in 2000, according to Dealogic.

Kraft's offer was at an 18% premium to Unilever's closing share price on Thursday, Unilever said.

Unilever shares rose 13% after the companies' announcements, suggesting investors were not fully convinced the deal would happen. Kraft shares rose 11% on Wall Street.

Unilever's best-known brands include:

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Food: Ben & Jerry's; Bovril; Colman's; Cornetto; Flora; Hellmann's; I Can't Believe It's Not Butter; Knorr; Magnum; Marmite; Pot Noodle; Wall's

Drink: Lipton; Lyons tea; PG Tips

Household: Comfort; Domestos; Dove; Lynx; Persil; Radox; Sure; Surf; Timotei; Tresemme; Vaseline

Kraft Heinz brands include:

Food: Amoy; Heinz Ketchup; Heinz Soup; HP Sauce; Kraft Mac & Cheese; Lea & Perrins; Philadelphia; Weight Watchers Smart Ones

Drink: Capri Sun; Kool-Aid; Maxwell House

Still, analysts said Kraft was likely to return with another offer for Unilever, which reported net profit of 5.5bn euros (£4.7bn) last year.

"With Kraft Heinz saying it'll be coming back to the table, it looks like the initial offer was just to test the water," said Nicholas Hyett, equity analyst at Hargreaves Lansdown.

Mr Buffett's investment fund Berkshire Hathaway and Brazilian private equity firm 3G are major investors in Kraft.

Kraft merged with Heinz in 2015 to create one of America's biggest food companies.

In 2010, Kraft bought Cadbury for £11.5bn, but it no longer owns the UK chocolate maker after spinning it off in a company called Mondelez.