LONDON — Almost two years after it was created in a megamerger, the Kraft Heinz Company is going shopping again. And it is aiming high.

On Friday, the company said that it had offered to buy Unilever in a $143 billion deal that would potentially combine some of the world’s best known consumer brands. If it were to happen, Unilever consumer staples like Dove soap, Hellmann’s mayonnaise and Lipton tea would join forces with Kraft Heinz’s Oscar Mayer meats, Heinz Ketchup and Kraft Macaroni & Cheese.

Kraft said that its offer had been declined, but that it looked forward to “working to reach agreement on the terms of a transaction.”

Unilever, however, said that the proposal “fundamentally undervalues” the company, and that it saw “no merit, either financial or strategic,” for the deal. It said it saw no basis for further discussions.

The Financial Times’s Alphaville blog earlier reported the offer.

“The main benefits from such a deal would be major cost reduction as head offices and regional management could be merged,” said John Colley, a professor of practice in strategy and leadership at Warwick Business School in Coventry, England. “There would also be some purchasing benefits from increased buying power.”

“Market power would be much increased, as the major supermarkets would have little choice but to buy from the merged business,” he said.

The offer came as consumer-goods companies are being squeezed by fluctuating currency rates, such as the strong United States dollar in Kraft Heinz’s case, and higher prices for staples used in their products.

It would also signal further consolidation in the sector as makers of consumer goods push for more space in the public’s shopping carts.

The offer came just over a week after the British consumer-goods company Reckitt Benckiser, which makes Durex condoms and Air Wick fresheners, agreed to buy Mead Johnson Nutrition, the maker of Enfamil baby formula, in a $16.6 billion deal.

Kraft Heinz’s offer followed speculation late last year that it might make an offer for Mondelez International, the maker of Oreos and Ritz crackers.

Unilever is the fourth largest seller of packaged food worldwide — behind Nestlé, PepsiCo and Mondelez — and Kraft Heinz is the fifth, according to data from Euromonitor International. In addition to packaged foods, Unilever also is the second-largest consumer-goods maker behind Procter & Gamble based on sales.

Kraft offered to pay $50 a share in cash and shares, representing an 18 percent premium to Unilever’s closing price on Thursday, Unilever said.

The proposal is for $30.23 a share in cash payable in United States dollars and 0.222 in shares in the combined company.

“There can be no certainty that any further formal proposal will be made to the board of Unilever or that an offer will be made at all or as to the terms of any transaction,” Kraft said in a news release.

Under British takeover rules, Kraft would have until March 17 to announce its firm intention to make an offer for Unilever or walk away.

Unilever’s shares rose more than 13 percent in afternoon trading in London on Friday after the announcement.

The stocks of other major packaged food makers were down in early trading in New York on Friday on concerns about worsening sales outlooks.

Shares of the Campbell Soup Company declined 5 percent and shares of J.M. Smucker Company fell 3 percent after the companies reported declining sales in their latest quarterly results. General Mills stock also declined 3 percent as the company lowered its sales outlook.

The offer came nearly two years after 3G Capital and Warren Buffett combined Kraft with Heinz in a deal worth more than $80 billion. Mr. Buffett and 3G acquired Heinz in 2013 and together own about 51 percent of Kraft Heinz.

On Thursday, Kraft Heinz, based in Chicago and Pittsburgh, reported net sales of $26.5 billion, while saying it would continue its cost-cutting efforts, targeting pretax cost savings of $1.7 billion by the end of this year.

It employs people in more than 40 countries worldwide.

Unilever, which is based in London but traces its roots to the Netherlands in the late 1800s, has about 400 brands in the food, personal care and home-care markets that it claims are used by two billion people daily.

These include Axe body spray, Ben & Jerry’s ice cream, Colman’s Mustard, Surf detergent and Vaseline.

Last month, the company reported 52.7 billion euros, or about $56 billion, in sales in 2016.

Correction: February 17, 2017

An earlier version of this article misspelled part of a name Kraft product. As the jingle goes, “My bologna has a second name, it’s M-A-Y-E-R,” not Meyer.