STOCKHOLM (Reuters) - The Swedish government will look into tightening sexual assault laws after a series of attacks at music festivals over the last week, Prime Minister Stefan Lofven said on Tuesday.

Swedish television reported the police were investigating 15 allegations of rape and around 40 of sexual assault at two recent music festivals.

"We are going to look at the laws on sex crimes," Lofven told Swedish TV.

"In addition, it is also important that we continue to make sure the police, prosecutors and other authorities get better at investigating these crimes so that we make sure we actually convict the perpetrators."

Mattias Grenestam, who is heading the preliminary police investigation into reported attacks at a festival in Bravalla, about 140 kilometers south-west of Stockholm, said the suspects were individuals of different ages acting alone.

"They can not be identified as part of any group," he told daily Dagens Nyheter.

Police in Karlstad, about 300 kilometers west of Stockholm and where the other music festival took place, initially identified those suspected of the sexual attacks as a gang of seven or eight unaccompanied migrant youths.

However, Karlstad police told Swedish radio that suspects included both migrant youths and others.

"So it is a bit too early to say what the common denominator is," Inspector Urban Bengtsson told Swedish radio.

Swedish police could not immediately be reached for comment.

Earlier this year, police launched an investigation into allegations that officers covered up accusations of sexual assault by mostly migrant youths at a music festival in Stockholm last year.

Sweden faces a backlash among many voters after a record 163,000 asylum seekers arrived last year, boosting support for the far-right Sweden Democrats, which polls show is the third biggest party.

(Reporting by Simon Johnson and Johan Sennero, editing by Larry King)