The number of Americans filing for unemployment benefits unexpectedly rose for a third straight week last week, likely as some automakers closed assembly plants for the annual summer retooling.

Initial claims for state unemployment benefits increased 4,000 to a seasonally adjusted 248,000 for the week ended July 1, the Labor Department said on Thursday. Data for the prior week was unrevised.

Economists polled by Reuters had forecast first-time applications for jobless benefits falling to 243,000 in the latest week.

It was the 122nd straight week that claims remained below 300,000, a threshold associated with a healthy labor market.

That is the longest such stretch since 1970, when the labor market was smaller. The labor market is near full employment, with the jobless rate at a 16-year low of 4.3 percent.

The four-week moving average of claims, considered a better measure of labor market trends as it irons out week-to-week volatility, rose 750 to 243,000 last week.

A Labor Department official said there were no special factors influencing the claims data. Claims for six states and a territory, including California and Alabama, were estimated because of Tuesday's Independence Day holiday. That probably did not contribute to last week's increase as some of the estimates

showed a decrease in applications.

Unadjusted claims for Michigan increased 1,159 last week.

Automakers normally shut assembly plants for annual retooling at the start of July, which tends to push up claims.

Applications are likely to remain elevated as some companies like General Motors (GM.N) embark on extended summer shutdowns to deal will slower sales, which have led to an inventory bloat.

Motor vehicle manufacturers reported on Monday that auto sales fell in June for a fourth straight month. Even before the annual summer plant closures, automakers have been laying off workers in response to the softening demand.

Outside the auto sector, the labor remain strong, with

record high job openings. Labor market tightness contributed to the Federal Reserve raising interest rates last month for the second time this year.

Economists expect another rate hike and the U.S. central bank to start reducing its $4.2 trillion portfolio of Treasury bonds and mortgage-backed securities later this year.

Thursday's claims report also showed the number of people still receiving benefits after an initial week of aid increased 11,000 to 1.96 million in the week ended June 24. The so-called continuing claims have now been below 2 million for 12 straight weeks, pointing to diminishing labor market slack.

The four-week moving average of continuing claims rose 6,750 to 1.94 million, remaining below the 2 million mark for 10 consecutive weeks.

Reuters (Reporting by Lucia Mutikani; Editing by Andrea Ricci)