Japan's yen had a rollercoaster week amid suspected intervention. Here's what you need to know

The Japanese yen weakened to levels not seen in 34 years against the U.S. dollar on Monday, only to rebound and likely clock its best week in more than a year. Here is what happened.

The yen touched 160.03 against the greenback on Monday, for the first time since 1990, but strengthened to 156 levels later that day amid speculation about an intervention by Japanese authorities.

On Wednesday, the currency strengthened by more than 2% to trade near 153 against the dollar, which is also likely to have been caused by an intervention, according to some market analysts.

Japanese authorities are yet to issue an official statement confirming their role in propping up the currency.

"The government has been refusing to disclose whether they've been intervening or not, but I don't think many people have any doubts," Nicholas Smith, Japan strategist at CLSA, told CNBC.

The yen is now trading at 152.90 against the dollar.

Analysts at Bank of America Global Research said the size of the first suspected intervention could have been between 5 trillion and 6 trillion yen ($32.7 billion to $39.2 billion), based on Bank of Japan data.

BofA Research also said that the size of the second likely intervention could have been smaller than the first.

Until the yen hit 160, several analysts had estimated levels between 155 and 160 to be the "line in the sand" for the BOJ and Japan's Ministry of Finance to intervene.

The weakness in the yen had persisted after the BOJ's monetary policy decision last Friday and in spite of warnings from Japanese authorities.

The yen had lost 7.3% as of Monday's low, since the Bank of Japan's historic meeting in March, when it ended the world's only negative rates regime.

But the first suspected intervention came only after the