Affiliated Managers Group Inc. [AMG] announced Monday it bought a stake in a London fund manager as the Boston company continues to look to expand internationally.

AMG, which owns a stake in Third Avenue Management, hedge fund firm AQR Capital Management and others, announced it was buying Artemis, a London fund manager, from BNP Paribas’ Fortis Bank. The deal, which is expected to close at the beginning of the second quarter, will leave AMG with a majority stake in Artemis, with the fund manager's management team taking an equity ownership stake. The price was not disclosed.

The acquisition of Artemis, which had $16 billion in assets under management at the end of last year, marks the fourth such deal for AMG in the past six months, according to Sean M. Healey, AMG’s president and chief executive officer.

“We have seen a real acceleration of deal activity,” he said during the company’s earnings conference call on Monday.

Last year, AMG bought a stake in Harding Loevner, a global and emerging markets equity manager, Value Partners, which extended AMG's presence into Asia, and manager-of-managers Aston Asset Management.

Darrell W. Crate, the company’s chief financial officer, said AMG is “positioned to make additional, significant new investments” this year. He said the company could make up to $750 million worth of acquisitions without needing to raise new capital.

Healey said the pipeline for more deals this year is “substantial” for AMG.  The company, which already owns stakes in money manager Third Avenue Management, hedge fund firm AQR Capital Management and others, plans to continue to look for ways to expand internationally by acquiring stakes in asset managers in Europe and Asia, Healey said. As of Dec. 31, AMG had $231 billion of assts under management.

Also on Monday, AMG reported a better-than-expected fourth-quarter profit, helped by strong performance at some of the asset managers that it owns a stake in.  In the fourth quarter, it reported a net income of $24.6 million, or 55 cents per share, compared with a loss of $83.7 million, or $2.12 per share, a year earlier. It beat analyst estimates by a penny, according to Thomson Reuters.

Healey said that AMG’s asset management units had “excellent relative performance and improving client flows” in the fourth quarter. He said equity and alternative investments saw outflows for much of last year, but “in the fourth quarter and so far in 2010 we are seeing things reverse. … Investors are moving to actively managed equity products and alternatives.”

“We feel good about how our business is positioned for 2010 and beyond,” Healey said. “We are positioned for strong and increased growth.”