Jack Antonoff fires up at Lorde heckler: 'That motherf*****'

Jack Antonoff has leapt to Lorde's defence, firing up at a heckler during a recent charity show in New York.

The incident comes after Antonoff denied rumours he was dating the Kiwi pop star, following his break-up with Lena Dunham.

Lorde was performing with Antonoff at the fourth annual all-star Ally Coalition charity event when a heckler took aim at her over the cancellation of a show in Israel.

Lorde was supposed to have performed in Tel Aviv later this year but cancelled the show following an outcry from those accusing her of taking sides in the ongoing Israel-Palestine conflict.

During the charity show, Lorde complimented fans while perched on a piano stool next to Antonoff, telling them: "You guys are so nice".

A heckler yelled back: "In Israel they're nice also."

Antonoff fired up at the comment, standing up and stopping the show.

He draped an arm around Lorde and bellowed: "Oh come on. No, hold on. We've raised a shit-ton of money tonight. F*** that negativity.

"That motherf***er better donate a couple ten thousands dollars more to this shit," he continued.

Lorde thanked Antonoff afterward: "I appreciate it. Thank you so much."

The incident comes after Antonoff took to Twitter to deny rumours he and Lorde had started dating after his break-up with Dunham.

He wrote on Twitter: "I'm not seeing anyone." His tweet was liked by Lorde.

The pair became friends after spending a year working on Lorde's second album Melodrama together.

The album has been nominated for a best album Grammy, which will be awarded at Monday's ceremony.