OSLO, March 13 (Reuters) - Three brothers and their mother have been remanded in police custody for up to four weeks on suspicion of taking part in the bombing of the U.S. embassy in Oslo last week, a Norwegian court said in a ruling on Friday.

The U.S. embassy was hit by an explosion on Sunday and police later said they had apprehended the suspects, accusing them of a "terror bombing" intended to kill or cause significant damage.

The powerful early-morning blast from an improvised explosive device (IED) damaged the entrance to the embassy's consular section but caused no injuries, Norwegian authorities have said.

One of the men has admitted to placing a device, while the three other suspects have denied involvement, their lawyers have said.

(Reporting by Terje Solsvik)