July 19 (Reuters) - Top U.S. carriers including Delta

Air and United Airlines are restoring some

operations on Friday after a technical issue related to an IT

vendor forced multiple carriers to ground flights.

However, delays and cancellations were expected to persist

throughout the day, as airlines try to fully recover from the

impact of the outage that upended their flying schedules and

affected thousands of passengers.

More than 1,400 flights were cancelled across the U.S., with

nearly 4,000 delayed, as of 10:00 am ET on Friday, according to

data tracker FlightAware.

It was not clear if the groundings reported by the major

U.S. airlines were related to outages at Microsoft ( MSFT ) and

cybersecurity firm CrowdStrike ( CRWD ) that hit banking,

healthcare and a number of other sectors globally on Friday.

Delta and United said they were resuming some flights but

expected additional delays and cancellations. The airlines also

issued travel waivers for impacted passengers.

Peer American Airlines ( AAL ), which had earlier issued a

ground stop notice, said it had safely re-established

operations.

While American, Delta and United did not name the vendor,

smaller carrier Frontier Airlines said that a "major

Microsoft ( MSFT ) technical outage" hit its operations temporarily.

The issue stemmed from a defect found in a CrowdStrike ( CRWD )

content update for Microsoft Windows hosts, the cybersecurity

firm's CEO George Kurtz said on Friday.

The U.S. Federal Aviation Administration said in an emailed

statement it was closely monitoring the technical issue

impacting IT systems at U.S. airlines and that several airlines

had requested its assistance with ground stops.

Parcel delivery firm FedEx ( FDX ) said it faced substantial

disruptions throughout its networks, while peer United Parcel

Service ( UPS ) also warned of potential delivery delays.

Microsoft ( MSFT ) said its outage started at about 6 pm ET on

Thursday, with a subset of its customers experiencing issues

with multiple Azure services in the Central U.S. region.

Azure is a cloud computing platform that provides services

for building, deploying, and managing applications and services.

(Reporting by Maria Ponnezhath, Shivani Tanna and Shivansh

Tiwary; Additional reporting by Chandni Shah, Nathan Gomes,

Surbhi Mishra, Angela Christy and David Shepardson; writing by

Abinaya Vijayaraghavan and Shubham Kalia; Editing by Nivedita

Bhattacharjee and Sriraj Kalluvila)