EU regulators on Wednesday opened a detailed probe of Dutch technology group TomTom's takeover of Dutch firm Tele Atlas on concerns the deal could stifle competition in the market for hand-held navigation devices.

The European Commission said it would rule by mid April whether to allow the 2.9-billion-euro (4.3-billion-dollar) takeover of Tele Atlas, a leading maker of digital maps, by TomTom, which makes portable navigation devices.

The European Union's top competition watchdog said it had "serious doubts" the deal would "lead to a significant impediment to effective competition."