Labor market churn picked up slightly in February, the Bureau of Labor Statistics reported Tuesday morning, but the pace of hiring and firing remains far below the levels that prevailed before the financial crisis that began six years ago.

The number of job openings crossed the 4 million mark, rising from 3.9 million in January to 4.2 million in February, according to the BLS monthly Job Openings and Labor Turnover Survey. Openings had fallen the previous two months.

The improvement meant that the number of unemployed workers per job opening in the U.S. fell from 2.6 to 2.5. That ratio has fallen from a high of nearly 7 in late 2009, but still remains well above 2005-2007 levels, when there were never more than two unemployed workers for every opening.

The number of hires also inched up, from 4.5 million to 4.6 million. The hiring rate, however, remained unchanged at 3.3 percent — that rate hasn't budged since the fall.

Hiring peaked at 5.5 million in late 2006 before slowing and then dropping precipitously after the financial crisis to 3.6 million in 2009.

Total job separations for the month declined slightly, from just above to just below 4.4 million. The number of voluntary quits, however, went in the opposite direction, rising to 2.4 million. More quits is usually taken as a sign of labor market health, as quits reflect workers' confidence in the labor market.

Overall, Tuesday's data suggests ongoing slow but steady improvement for a badly weakened U.S. labor market.

That improvement continued throughout February, a month many analysts said was otherwise affected by worse-than-usual winter weather throughout much of the country. A pick-up in job creation and hiring as the weather warms in future months would suggest that the gains would have been even stronger in the absence of the snowstorms that slowed commerce in the winter months. But the trend for labor market churn in the private sector has so far proved impervious to all kinds of weather, politics and other effects.

The BLS' JOLTS release is separate from its monthly jobs report, which includes information on job gains taken from a survey of businesses and governments. In that separate survey's data, the U.S. economy added 197,000 jobs in February. That number was slightly better than the labor market recovery average, which is about 180,000 jobs a month. The initial release for March showed a smaller gain of 192,000.