Japan's current account surplus expanded 4.2 percent in August from a year earlier, official data showed Tuesday, the first monthly rise since last year's quake-tsunami disaster and nuclear crisis.

The surplus in the current account, the broadest measure of Japan's trade with the rest of the world, stood at 454.7 billion yen ($5.8 billion) in August, the finance ministry said, slightly beating market expectations.

That was the first monthly expansion since February 2011, a positive sign for Japan's economic recovery after last year's March 11 disasters triggered the worst nuclear accident in a generation.

The latest monthly reading was higher than forecasts by economists surveyed by Dow Jones Newswires and the Nikkei business daily, who estimated a surplus of 442.0 billion yen.

But export weakness remained a risk to the world's third-largest economy as a slowdown in the global economy and a strong yen weighed on demand for Japanese products overseas, analysts said.

The current account measures trade in goods, services, tourism and overseas income.