LONDON (Reuters) - British Labour Prime Minister Keir Starmer has been urged by former defence secretaries and an ex-premier to allow Ukraine to use long-range missiles inside Russian territory even without U.S. backing, the Sunday Times reported on Saturday.

According to the Sunday Times, the call came from five former Conservative defence secretaries - Grant Shapps, Ben Wallace, Gavin Williamson, Penny Mordaunt and Liam Fox - as well as from ex-Prime Minister Boris Johnson.

They warned Starmer that "any further delay will embolden President Putin", the Sunday Times said.

Ukrainian President Volodymyr Zelenskiy has been pleading with allies for months to let Ukraine fire Western missiles including long-range U.S. ATACMS and British Storm Shadows deep into Russia to limit Moscow's ability to launch attacks.

Starmer and U.S. President Joe Biden held talks in Washington on Friday on whether to allow Kyiv to use the long-range missiles against targets in Russia. No decision was announced.

Some U.S. officials are deeply skeptical that allowing the use of such missiles would make a significant difference in Kyiv's battle against Russian invaders.

President Vladimir Putin has said the West would be directly fighting Russia if it allowed Ukraine to strike with Western-made long-range missiles.

(Reporting by Catarina Demony; Editing by David Gregorio)