Mail Online, Associated Newspapers' online network, has overtaken the Huffington Post to become the second most popular news website in the world in March, according to new figures from metrics firm comScore.

Arianna Huffington's groundbreaking news and opinion website, which was bought by AOL for $315m (£193m) in February, was leapfrogged by Mail Online, which is now second only to the New York Times in ComScore's "newspapers" category.

Mail Online has grown exponentially in the past three years, in part due to its showbiz-laden front page, but also because of its focus on US news. Associated has been hiring editorial staff in New York and Los Angeles to feed its online news operation.

According to comScore, Mail Online reported a 27% rise in unique visitors between February and March, to 39,635,000. Huffington Post, meanwhile, recorded a 20% lift, to 38,429,000 unique visitors.

Mail Online remains the most popular UK newspaper website. However, the site suffered a slight drop in UK online traffic in February – the first in a period of sustained growth, according to the latest figures from the Audit Bureau of Circulations Electronic.

The New York Times was still by some distance the most popular English-language news site in March. The market-leading title benefited from a remarkable month in world news, reporting a 41% rise in traffic on February to a record 61,964,000 unique visitors.

However, that figure is expected to drop after the New York Times introduced its long-delayed metered subscription service on 28 March, although NYT executives have been careful to only charge the heaviest users of the site.

There will be three charging options for four weeks' access, with the cheapest at $15 for the NYT website and its smartphone app; $20 for the website and the tablet app; and $35 for all devices.

The Tribune Newspapers network of websites were the fourth most popular for March, with 34,624,000 unique visitors, the comScore figures reveal.

Guardian.co.uk, which is part of the group that publishes MediaGuardian.co.uk, was the fifth most read English-language news site in the world, with 30,891,000 users. In March, the Guardian unveiled plans for an expanded digital operation in the US, which will be headed up by Guardian.co.uk editor Janine Gibson.

The Guardian has an US online audience of about 8 million users, according to comScore metrics from February 2011.

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