By Vidya Ranganathan and Kevin Buckland

SINGAPORE (Reuters) - The Japanese yen made a thumping 4 yen jump for a second straight session on Monday on suspected early intervention by the Bank of Japan, but struggled to hold its gains against a robust U.S. dollar.

The yen hit a low of 149.70 per dollar in early deals before being swept to a high of 145.28 within minutes in a move that suggested the BOJ had stepped in for a second successive day. The currency, however, dropped back to near 148 soon.

"It's blindingly obvious that the BOJ is intervening," said Ray Attrill, head of FX strategy at National Australia Bank (OTC:) in Sydney. "Dollar-yen wouldn't be moving like this otherwise."

Friday's intervention, which policy sources confirmed, came as the dollar hit a fresh 32-year high of 151.94 yen and triggered a rally of more than 7 yen for the Japanese currency to 144.50 per dollar.

That was the second confirmed instance of Japanese intervention, although traders suspect the BOJ had stepped in on other occasions in the past month to shore up a currency that has tumbled 22% this year against the dollar.

Analysts at Goldman Sachs (NYSE:) said the intervention helps the BOJ limit yen depreciation and gives it time on its ultra-low interest rates' policy, which is at odds with a global wave of tightening and has widened the gap between U.S. and Japanese interest rates.

"The yen’s beta to U.S. rates has fallen since the first intervention operation, and repeated intervention steps will likely keep it that way for a while, in part by inducing two-way volatility into dollar/yen," Goldman wrote last week.

"While sub-optimal and unsustainable in the medium term, we think this policy mix could be in place for some time."

The was up 0.063% at 111.87, with the euro down 0.02% to $0.9858.

Sterling was last trading at $1.1343, up 0.36% on the day, helped in part by weekend news that former prime minister Boris Johnson has withdrawn from Monday's contest to replace Liz Truss, who was forced to resign after she launched an economic programme that triggered turmoil on financial markets.

Former Chancellor Rishi Sunak has emerged as the clear frontrunner to become Britain's next prime minister.

The Australian dollar was down 0.4% versus the greenback at $0.6370, while the was up 0.16% on its U.S. peer at $0.576.

In cryptocurrencies, bitcoin last rose 2.08% to $19,578.40.

(This story has been corrected to fix garbled words in fourth paragraph)