Microblogging service Twitter has reportedly closed a $15 million Series B funding round, according to Om Malik of GigaOM.

Malik estimates that it will bring the company's valuation to about $80 million and that the round is led by a new investor rather than existing investor Union Square Ventures (though the latter is participating). CNET News.com originally reported late in April that Twitter had signed a term sheet for either $15 or $20 million.

Rumors peg the new lead investor as Boston-based Spark Capital. An independent source hinted to CNET News.com that this is likely indeed the case.

Twitter Reportedly Gets $15Million Funding [news.cnet.com]