The partner of an American passenger on board Malaysia Airlines flight MH370 has received death threats and several bizarre telephone calls since the plane went missing on March 8, NBC News reported.

Sarah Bajc, the partner of Philip Wood, had also been robbed twice since the disappearance of the plane.

The United States Federal Bureau of Investigation (FBI) is now looking into the "frightening incidents" that have left Bajc upset.

Bajc told NBC News that she received an instant message warning that "I'm going to come and kill you next" about two weeks after the Malaysia Airlines plane disappeared.

Several pornographic images and creepy phone calls were also received from the same China-based number, she said.

“It was just another straw on the camel’s back, very upsetting," Bajc told NBC News.

According to Bajc, the calls and messages began shortly after her apartment was broken into for the first time, midway into the second week after the flight disappeared.

“Whoever came wasn’t very careful because I’m a real neat freak, so it was immediately apparent to me that some things had been moved,” she told NBC News.

“My housekeeper was out of town so it couldn’t have been her and I got home before my son got back. The password on my safe had been reset which happens when you try the wrong code three times."

Bajc told NBC News the second break-in happened a couple weeks later.

"My neighbour saw two people leaving my apartment. I have no illusions of privacy here (in Beijing).”

She told NBC News that the calls stopped after an FBI agent assigned to help her and the Wood’s family was informed.

Bajc has been spearheading the call by relatives for investigators to release raw data on the missing aircraft.

She had hit out at Malaysian officials, saying Malaysia's acceptance of the data analysis by British satellite firm Inmarsat had not been put to scientific scrutiny.

"They have failed to share why they would accept a single source (Inmarsat) for analysis utilising a never-before-attempted method as their sole ground for determining that the plane is under the water and all lives lost," the Wall Street Journal had quoted her email sent to the media.

She had also taken a swipe at Prime Minister Datuk Seri Najib Razak, who in an exclusive interview with CNN, had announced that a preliminary report would soon be made public.

"I'm just so astounded by this new shift that the prime minister is taking... He's reading from a script sheet that some qualified, professional PR person has put together for him," Bajc had told CNN.

She is also leading an effort to appeal to shareholders of aircraft manufacturer Boeing to pressure for answers after failing to get any information from Putrajaya and Malaysia Airlines to lingering questions over the investigation into the missing flight.

Prior to this, Bajc had also received an email from a senior Fox executive who offered to raise millions of dollars if she agreed to waive future compensation claims. The Fox executive was later sacked by the network.

Bajc was in the process of moving from Beijing to live with her partner, a 50-year-old IBM Malaysia employee.

Wood is among the 239 people on board the missing plane. He was flying from Kuala Lumpur to Beijing to meet Bajc when the Boeing 777-200ER vanished.

Extensive air and sea searches over vast stretches of the Indian Ocean have failed to find any sign of the aircraft. – May 11, 2014.