Two letter bombs have exploded in the Netherlands.

One of the blasts happened at an ABN Amro Bank mail-sorting office in Amsterdam.

The other occurred 225km away at Kerkrade in the postroom of Japanese electronics group Ricoh.

Police reported no injuries and said they were investigating whether the blasts were linked to a string of letter bombs intercepted in the country since early January.

Dutch news agency ANP said the sender of the letters had demanded payments in bitcoin.

Dutch police declined to provide details, but confirmed that extortion was among the motives under investigation.

An employee in the Amsterdam sorting office heard a hissing sound as they were about to open a letter.

Local police said on twitter: "The employee threw the letter away and there was a small explosion."

ABN's chief executive, Kees Van Dijkhuizen, said he had spoken to the man who had handled the letter at the sorting centre, located in the western outskirts of Amsterdam.

"Good news is that he is not wounded, bad news of course is that these things happen and that our people have to deal with it," Mr Dijkhuizen told journalists.

The second explosion in the southern town of Kerkrade, on the border with Germany, was at the offices of Ricoh, a Japanese electronics company.

"Thankfully there were no injuries, but those involved are of course very shocked," Ricoh said in a statement.

The blast caused some damage and the facility was closed for forensic analysis, police said.

They have been investigating a spate of letter bombs since 3 January, which they said appeared to have been sent by the same person. They were all intercepted before they could explode.

Previous targets have included a hotel, a petrol station, a garage, an estate agents and a bill collection service.