European stocks declined, paring their biggest weekly gain in six months, after Federal Reserve Chair Janet Yellen underscored the persistence of labor-market slack in the U.S. economy and as investors watched rising tensions in Ukraine.

Piraeus Bank SA and Banca Monte dei Paschi di Siena SpA gained at least 2.8 percent as a gauge of lenders advanced for a second day. Essentra Plc climbed 3.1 percent after JPMorgan Chase & Co. raised its rating on the U.K. maker of items from toothpaste tubes to packaging tape. CGG SA and Fugro NV lost at least 2 percent as oil and gas companies retreated.

The Stoxx Europe 600 Index slipped 0.3 percent to 336.5 at 4:30 p.m. in London. The gauge earlier dropped as much as 0.7 percent after Russian aid trucks entered Ukraine without consent from Kiev. The Stoxx 600 rallied 2.1 percent this week as investors bet that industrial slowdown in the euro area will increase pressure on the European Central Bank to introduce asset purchases known as quantitative easing.

“We’re so used to Yellen being an arch dove, anything less than that is treated with some disappointment,” Michael Ingram, a market strategist at BGC Brokers LP in London, said by telephone. “But it does look like the market is edgy particularly in light of the Fed minutes we saw earlier in the week. The center of gravity in terms of a rate decision does seem to be moving toward an earlier rise.”

Labor Slack

In remarks that appeared to be in line with the minutes of the Fed’s latest policy meeting, Yellen said Friday that slack remains in the U.S. labor market even after gains made during the five years of economic recovery. Stocks briefly pared losses after her comments.

“The economy has made considerable progress in recovering from the largest and most sustained loss of employment” since the Great Depression, Yellen said in a speech at the Kansas City Fed’s annual economics conference in Jackson Hole, Wyoming. Even so, she underscored the Federal Open Market Committee statement last month that “underutilization of labor resources still remains significant.”

Yellen also said the Fed’s assessment of employment slack has become challenging and there is no simple recipe for appropriate policy.

ECB President Mario Draghi will address policy makers, academics and investors at Jackson Hole after the European markets close. Bank of Japan Governor Haruhiko Kuroda will take part in a panel discussion Saturday.

Russian Trucks

More than 150 trucks carrying humanitarian aid from Russia crossed into Ukraine’s border today and headed for the city of Luhansk. Ukraine said the move amounted to an invasion as the convoy entered without its consent. Ukraine allowed the vehicles to proceed after failing to discuss its safety with the Russian side, the Foreign Ministry in Kiev said in a statement.

National benchmark indexes fell in all the western European markets except Greece. The U.K.’s FTSE 100 Index slipped less than 0.1 percent, France’s CAC 40 retreated 0.9 percent, and Germany’s DAX lost 0.7 percent. The ASE Index in Athens climbed 1.1 percent, taking its rally since a 10-month low on Aug. 8 to 10 percent.

A measure of banks rose to the highest level this month. Piraeus Bank rallied 4.2 percent to 1.50 euros, and Alpha Bank AE gained 2.7 percent to 65 euro cents. Monte Paschi climbed 2.8 percent to 1.09 euros.

Essentra climbed 3.1 percent to 853.5 pence. JPMorgan raised its rating on the shares to overweight from neutral, saying potential mergers and acquisitions may increase investor returns in the near term.

Lonmin, CGG

Lonmin Plc climbed 2.2 percent to 217.5 pence. Goldman Sachs Group Inc. raised its recommendation on the platinum producer to “conviction buy” from neutral, saying that concerns over the company’s balance sheet and operations are overdone.

CGG declined 4.6 percent to 6.46 euros, while Fugro fell 2.2 percent to 28.06 euros. A gauge of oil-and-gas companies in the Stoxx 600 retreated 0.6 percent.

IG Group Holdings Plc lost 3.2 percent to 598.5 pence. The U.K.’s biggest spread-betting firm may see revenue drop as much as 15 percent in the first quarter as its U.S. peer FXCM Inc. reported retail volumes slumped 39 percent in June and 33 percent in July, Barclays Plc wrote in a note.

The volume of shares changing hands in Stoxx 600-listed companies was 16 percent below the 30-day average for this time of the day, according to data compiled by Bloomberg.