The world's richest man, Elon Musk, sent Twitter into a frenzy on Monday with a single tweet. 

"If I die in mysterious circumstances, it's been nice knowin ya," he wrote in a tweet that received more than half a million likes in a matter of hours. 

Musk's tweet appears to reference a perceived threat from Russia over the tech billionaire's decision to send SpaceX-run satellite internet service to Ukraine. 

Musk sent his emergency Starlink receivers to parts of war-ravaged Ukraine where internet has been cut and locals have no way of communicating. 

The former deputy prime minister of Russia and the country's space boss, Dmitry Rogozin, didn't take kindly to the move, reportedly telling Russian state media that Musk "will be held accountable like an adult". 

"It turns out the internet terminals of Elon Musk's Starlink satellite company were delivered to the militants of the Nazi Azov Battalion of the Ukrainian Marines in Mariupol by military helicopters," Rogozin allegedly wrote in a message shared by Musk on Monday. 

"According to our information, the delivery of the Starlink equipment was carried out by the Pentagon. 

"Elon Musk, thus, is involved in supplying the fascist forces in Ukraine with military communication equipment. And for this, Elon, you will be held accountable like an adult – no matter how much you'll play the fool." 

Musk's "If I die" tweet followed minutes later, stirring up his followers. 

"Double up (or even 10x) on security. We need you around, Elon," wrote YouTuber Dave Lee. 

Others tried to get the hashtag #KeepElonSafe trending. 

Rogozin, who is the head of Russia's space agency, is no stranger to provocations with the United States. 

He has been an outspoken critic of sanctions imposed against Russia following its invasion of Ukraine and warned that Russia could destroy Nato countries with nuclear weapons in "half an hour". 

"In a nuclear war, Nato countries will be destroyed by us in half an hour," he said earlier this week. 

"But we must not allow it, because the consequences of the exchange of nuclear strikes will affect the state of our Earth. 

"Therefore, we will have to defeat this economically and militarily more powerful enemy with conventional armed means." 

The comments from Musk come as the newest owner of Twitter reveals his plans for the platform. 

The Tesla founder launched a successful bid to buy the social media platform for US$44 billion last month. 

The New York Times is reporting that Musk has presented a pitch to investors this week claiming he would increase the company's annual revenue, which was $5b last year, to $26.4b in 2028. 

According to the pitch, Musk also expects to grow Twitter's user base from 217 million at the end of last year to almost 600 million in 2025 and 931 million in 2028. 

He wants the average revenue per user to be $30.22 in 2028, up from $24.83 last year. 

As for the current Twitter Blue, where users subscribe for $4.49 a month to customise their experience, Musk expects 159 million users within six years. It was only launched last year. 

Other key points included bringing in $15 million from a payments business in 2023 and $1.3 billion by 2028. It is unknown what it involves. 

The company will also rely on advertising less, falling to less than 50 per cent of its revenue, according to the pitch.