The sudden and surprising airspace closure over El Paso, Texas, on Wednesday stemmed from the Pentagon's plans to test a laser for use in shooting down drones used by Mexican drug cartels, according to three people familiar with the situation.

The restriction covered all flights to and from the airport up to a height of 18,000 feet, and initially remained in place until 2.

Key US senators are seeking answers from the US Federal Aviation Administration and the Pentagon over what led to the sudden closure of airspace around El Paso, Texas, earlier this week.

Various theories circulate in the wake of the El Paso, Texas airspace closure. Federal government handling widely criticized.

The FAA said the area around the Texas border town would be closed for "special security reasons".

New evidence suggests the CBP's use of a military anti-drone laser triggered an airspace shutdown initially attributed to Mexican cartels.