FRANKFURT, Jan 21 (Reuters) - Changing circumstances including plunging oil prices and turmoil in global markets mean the European Central Bank would lose credibility if it did not review its monetary policy stance in March, ECB chief Mario Draghi said on Thursday.

“The measures we decided in December were entirely appropriate -- and have been effective -- based on the circumstances that were prevailing at that time,” Draghi told a news conference.

“Since then these circumstances have changed,” Draghi said, noting the 40 percent fall in oil and change in the euro’s exchange rate since the ECB’s last staff economic projections as well as the selloff in markets and geopolitical factors.

“So now these conditions have worsened, and I think the credibility of the ECB would be harmed if we were not ready to review and possibly reconsider our monetary policy stance when we will have full information.”

The extension at December’s ECB policy meeting of asset purchases and the decision to reinvest proceeds had added some 680 billion euros of liquidity to the programme, about two-thirds of its original size, Draghi said.

He also reiterated the Governing Council’s “power, willingness and determination to act”, “and the fact that there are no limits to our action -- “within our mandate of course”.