Tokyo was the most active market for office property transactions in the first half of this year, buoyed by major deals in prime properties, a real estate market research firm said.

Tokyo's property market was hit hard as the global credit crunch pushed down property values and squeezed financing, driving investors away. But they began returning earlier this year, hoping to scoop up properties at attractive prices.

The biggest office transaction during the January-June period was American International Group Inc's $1.2 billion sale of its main building to Nippon Life Insurance Co.

The second-largest was Mitsubishi Estate Co's acquisition of the Asahi Seimei Otemachi Building in Tokyo's central business district for $811 million, data compiled by Real Capital Analytics showed. The firm counted 80 deals worth $10 million or more in Tokyo's office market in the January-June period.

Of the top 10 office property transactions, five were in Tokyo, with London the next most active market followed by Paris and Seoul, said the New York-based research firm.

Japan as a whole attracted a total $7.4 billion of investment in the January-June period, down 52 percent from the previous year, but topping the most active country ranking for the first time.

Britain came second with $5.79 billion in investment, followed by the United States with $5.22 billion, said Real Capital Analytics. (Reporting by Mariko Katsumura; Editing by Joseph Radford)