HOUSTON â€"  Two Houston-area sisters were among the 153 passengers who were killed when a passenger plane crashed in Nigeria Sunday.

The family of Jennifer and Josephine Onita tells MyFoxHouston the sisters were aboard the doomed flight that crashed Sunday into a neighborhood in Lagos, Nigeria's most populous city.

The family says the sisters had travelled to Nigeria to go to a wedding. Newscore reports the sisters are believed to be in their mid-twenties and lived in Missouri City, which is southwest of Houston. 

Both attended Texas universities, with Josephine Onita  attending the University of North Texas and Jennifer Onita attending Texas Tech.

Airline officials said Monday that the pilot of the doomed aircraft was also an American, though neither the pilot's name nor any details about him or her was released.

State Department spokesman Mark Toner said earlier in the day the department believes many Americans were aboard the plane, though it is too soon to know exactly how many.

"We're still, frankly, unable to provide a firm number," he said "I can also say that our consulate in Lagos is working both to notify the next of kin and also provide any appropriate consular assistance."

All of the 153 passengers and crew aboard the aircraft died, and it is believed more people were killed as it smashed into a two-level apartment building on the ground.

Among the dead passengers were six Chinese citizens, while the co-pilot was Indian, Nigerian civil aviation chief Harold Demuren said.

US officials are assisting with the investigation into the crash, which is expected to take months.

The 22-year-old plane is said to have been sold by Alaska Airlines three years ago and, according to an unnamed official cited by The Guardian, had experienced previous problems -- including two instances of smoke billowing from the cockpit.

The plane, which was flying to Lagos from the capital Abuja, was in use despite Nigeria's ban on aircraft over 20 years old.

Demuren said the pilots had called mayday before the crash, saying that both engines had failed. It is still unclear what caused the failure, with speculation ranging from faulty parts or a lack of fuel to a bird collision.

At least one of the plane's two cockpit recorders had been found, officials said.

Rescue workers had recovered at least 137 bodies by Monday evening, with most of those victims believed to be passengers in the plane, AFP reported.

Officials have turned their attention to the ruins of the two-story residential building, where more bodies are expected to be found.

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Newscore contributed to this report.