An American Airlines passenger jet with 64 people on board has crashed midair into a military helicopter while attempting to land at Reagan National Airport in Washington.

Emergency services in the city are searching the nearby Potomac River after the jet plummeted into the water just before 9pm on Wednesday night.

Officials have not said how many people died in the accident but have suggested that there may be no survivors. It is the first major commercial air crash in the US in 16 years.

Russian strongman Vladimir Putin apologized to Azerbaijan on Saturday for the crash of a civilian flight carrying passengers from Baku to Grozny in Russia-controlled Chechnya.

Putin had a phone call with Azerbaijani president Ilham Aliyev and “apologised for the tragic incident that occurred in Russian airspace and once again expressed his deep and sincere condolences to the families of the victims and wished a speedy recovery to the injured,” the Kremlin said.

Azerbaijan’s president on Sunday demanded that Russia admit responsibility for the incident that led to the Christmas Day crash of a passenger plane that killed 38 people and pay compensation to the government and affected families.

White House spokesman John Kirby has said the US has seen "early indications" that Russia may have been responsible for the downing of the Azerbaijan Airlines plane that crashed on 25 December, killing 38 people.

Mr Kirby did not elaborate further, but told reporters the US had offered assistance to the investigation into the crash.

The White House said preliminary evidence suggests that Russia‘s defense systems shot down a commercial flight originating in Azerbaijan. 

On Christmas Day, the plane, operated by Azerbaijan Airlines, was flying from Baku, the capital of Azerbaijan, to Grozny, the capital of Chechnya in Russia, when it crashed. Thirty-eight people were killed, and 29 survived. 

Evidence suggests the Azerbaijan Airlines flight that crashed in Kazakhstan on Christmas Day was brought down by Russia, the White House said Friday.

“We have seen some early indications that would certainly point to the possibility that this jet was brought down by Russian air defense systems,” National Security Council spokesman John Kirby told reporters. He said the evidence went beyond widely circulated images of the damaged aircraft, but he did not provide details.

An Azerbaijan Airlines flight that crashed in Kazakhstan on Wednesday, killing 38 people, was shot down by a Russian air defense system, Reuters reported Thursday.

The report cited four sources in Azerbaijan familiar with the investigation into the crash. One of the sources said preliminary results showed the plane was struck by a Russian Pantsir-S air defense system, and its communications were paralyzed by electronic warfare systems on the approach into Grozny, Reuters reported.

The Russian government has cautioned against promoting "hypotheses" about the cause of the crash of a Russia-bound passenger plane that killed 38 people in Kazakhstan on Wednesday.

Some aviation experts suggested that the Azerbaijan Airlines plane had been hit by air defence systems over the Russian republic of Chechnya and pro-government media in Azerbaijan quote officials as saying a Russian missile was responsible.

Azerbaijan held a day of mourning on Thursday for the dozens of victims of an airliner crash in Kazakhstan, as questions were being asked over the cause of the disaster.

The reasons that Azerbaijan Airlines flight J2-8243 came down are still unknown. Reuters reported Thursday that the plane was downed by a Russian air defense system, citing multiple unnamed sources in Azerbaijan with knowledge of the investigation.