SAO PAULO, June 2 (Reuters) - Brazilian beefpacker Marfrig Global Foods MRFG3.SA is increasing its stake in food processor BRF SA BRFS3.SA, financial blog Brazil Journal reported on Wednesday, putting the buyer very close to the threshold where it would have to make a public tender for all the company's outstanding shares.

Citing at least one source with knowledge of the matter, Brazil Journal said Marfrig has added to a 24% stake acquired last month, and that it was approaching a 30% holding via open market transactions.

Marfrig, which produces beef in the United States and Brazil, declined to comment on the veracity of the report, but its shares were up 4.3% on the Sao Paolo stock exchange in early afternoon trading.

BRF, the world's largest poultry exporter which also produces pork, declined to comment on the report.

Its shares have soared around 12% since Tuesday to trade at a 52-week high, but the company said in a securities filing on Wednesday that it was unaware of the reasons behind the sudden spike.

Marfrig has insisted it is only interested in a passive stake in BRF but its stake-building comes almost two years after previous failed merger talks between the two companies. Combined, the companies could be in a better position to take on industry leader JBS SA

Under BRF's by-laws, when an investor reaches ownership of 33.33% of the company's capital stock, it needs to launch a public tender for all of its remaining shares.