Police guarding the U.S. embassy in Brussels | Olivier Vin/AFP via Getty Images US embassy plans move out of downtown Brussels Relocation could take up to six years.

The U.S. embassy in Belgium and its diplomatic mission to the European Union are planning to move from their longtime headquarters near the EU institutions to a location outside of downtown Brussels, according to a U.S. government source.

Belgian newspaper L'Echo reported Thursday that the U.S. had agreed to buy a building previously occupied by bank insurer AXA in the leafy district of Watermael-Boitsfort, at the edge of the Brussels city limits about seven kilometers from downtown. The steel-and-glass building, in a verdant campus on Boulevard du Souverain, was constructed in 1970 for the Royale Belge insurance company.

The current U.S. compound is located about a kilometer from the Maalbeek metro station, the scene of a bombing in March that killed 16 people. According to a U.S. government official, the search for a new facility in Brussels had been going on for years, and was not directly related to the March attacks.

But, the source added, "There have been efforts all over the world to move embassies for broader security concerns."

After the purchase is completed the relocation from the current premises on Boulevard du Regent could take up to six years, said another U.S. government official, who declined to specify the new location. The report in L'Echo suggested the embassies could move to the new site in as little as two years, after an upgrade of the premises for security needs. But the U.S. source called that timetable "aggressive."

"We've been working in the current facility since World War II, we've outgrown these facilities as our engagement with Belgium and the EU has grown," said U.S. embassy spokesperson Elijah Waterman. "Therefore we've been looking for alternate sites for several years but we cannot comment on a specific location."