Spain's health minister warned that a seven-week decline in the national COVID-19 infection rate could have bottomed out after cases ticked higher in a handful of regions.
"We could be facing a possible change in trend," Carolina Darias told a news conference. "So maximum caution should be exercised to avoid a fourth wave."
The infection rate as measured over the preceding 14 days has fallen from a peak of nearly 900 cases per 100,000 people at the end of January to below 130 cases as authorities brought a post-Christmas third wave under control.
But the pace of decline has slowed recently, and infections inched higher on Wednesday to 127.9 cases per 100,000 from 127.8 cases a day earlier.
Madrid, Catalonia and seven other regions reported slight increases in the incidence, Health Ministry data showed, though the national rate remained at its lowest since August.
The ministry added 6,092 new cases, largely in line with recent increases and bringing the tally to 3.21 million. The death toll climbed by 228 to 72,793.