The European Central Bank kept interest rates on hold Thursday, leaving the key policy rate at 3.75%, as expected. The ECB didn't provide any rationale for the decision, but its president, Jean-Claude Trichet, will comment on the move at a press conference at 1230 GMT. ECB watchers will be listening for clues about future policy action, with most economists expecting rates to rise to 4.0% in June. Newswires Tuesday correctly predicted Thursday's verdict. Trichet is widely expected to reiterate that monetary policy remains on the "accommodative side," with interest rates "moderate." He is also expected to downplay recent benign inflation numbers, stressing that "upside risks" to price stability remain. The ECB aims to anchor inflation at a level "close to, but below" 2% over the medium term. Trichet is likely to reiterate that the ECB will "very closely" monitor developments, and act in a "firm and timely manner" in order to ensure price stability. Such language would point to a June interest rate hike. The ECB has developed a set of phrases to signal its future policy intentions, while insisting it doesn't pre-commit to any particular interest rate path. When Trichet has said that the ECB will "closely monitor" price developments, it has typically signaled that rates won't rise in the coming month. When Trichet has said the ECB will exercise "vigilance" in countering inflationary pressures, it has typically signaled a rate hike at the ECB's next monthly meeting. Any mention of the key word "vigilance" would come as a surprise to the markets and prompt a reaction from them, economists say.