Image copyright Getty Images Image caption FAA chief Steve Dickson

The US regulator for airline safety has said he is "pleased" with progress made by Boeing as it works to get its 737 Max plane re-approved for flight.

The aircraft has been grounded since March 2019, following two fatal crashes that killed 346 people.

Boeing recently said the jet might not return to service until mid-2020.

Federal Aviation Administration (FAA) chief Steve Dickson said his agency "has no set timeframe" to complete its review.

He issued the statement following a Reuters report that he had told airlines that Boeing's public timeline was "very conservative" and that re-certification could come before July.

The news sent shares in Boeing up 2% on Friday.

The firm has been in crisis since the crashes, which occurred within five months of each other - first in Indonesia in October 2018 and then in Ethiopia last March.

It is facing multiple investigations amid accusations that it sacrificed safety as it rushed to get its jets to customers.

The FAA has also been accused of failing its oversight duty, due to a too-cosy relationship with Boeing.

29 October 2018: A 737 Max 8 operated by Lion Air crashes after leaving Indonesia, killing all 189 people on board

A 737 Max 8 operated by Lion Air crashes after leaving Indonesia, killing all 189 people on board 31 January 2019: Boeing reports an order of 5,011 Max planes from 79 customers

Boeing reports an order of 5,011 Max planes from 79 customers 10 March 2019: A 737 Max 8 operated by Ethiopian Airlines crashes, killing all 157 people on board

A 737 Max 8 operated by Ethiopian Airlines crashes, killing all 157 people on board 14 March 2019: Boeing grounds entire 737 Max aircraft fleet

The grounding of the 737 Max, which had been Boeing's best-selling plane, is estimated to have cost Boeing more than $9bn already.

Last month, Boeing said it would halt production - a move that analysts say could shave 0.5% off US economic growth in the first three months of the year.

Suppliers have announced job cuts and airlines are grappling with schedule shifts. Many of the airlines have said they do not expect the 737 planes back in service before at least June.