MULTAN, Pakistan (Reuters) - Pakistani security forces appeared to be trying to dampen down reporting this weekend on the background of Tashfeen Malik, who mounted an attack alongside her husband that killed 14 people in California.

Three professors at Malik's university said they had been advised not to talk to the media, while men claiming to be from Pakistan's security agencies told reporters to drop their investigations into her background on pain of arrest.

An official at the interior ministry later said this was due to a "misunderstanding".

U.S. authorities are treating last Wednesday's mass shooting in San Bernardino as an "act of terrorism". Malik, 29, and husband Syed Rizwan Farook, 28, were killed two hours later in a shootout with police.

The Iraq- and Syria-based Islamic State jihadist group has claimed the couple as its followers, although it has not said it was in contact with them or that it directed the attack.

Malik was born in Pakistan but spent most of her life in Saudi Arabia before she came to the United States to marry her husband, a U.S. citizen. She had a degree in pharmacy from a university in Pakistan's central city of Multan.

On Sunday, three professors at Bahauddin Zakariya University, which Malik attended, said they had been instructed by security agencies not to speak to reporters.

One, who asked not to be named, said security officials visited the university on Saturday and removed records and pictures of Tashfeen.

"She was a very reserved person, a very quiet girl, she kept to herself," the professor said. "I could have never imagined she was capable of something like this. And there was nothing on the surface to suggest she had such extremist tendencies."

"I think this change in her mind, whenever it happened, must be very recent. The girl I remember ... she could not have the guts to do this."

Another former professor said he did not remember her at all. "She was probably not someone who stood out, academically or otherwise," he said.

Unspecified Offenses

Men claiming to be from security agencies, but who refused to provide identification, also sought to discourage Reuters from further reporting on Malik's background, threatening journalists with arrest for unspecified offences.

"Whether you consider this a request or a dictation (order), I would advise you not to pursue this story," one said.

Tim Craig, a reporter from the Washington Post, tweeted that police had prevented him from leaving his hotel in Multan.

"I've lost track of how many different security/intel officials I've had to talk to, copy my passport, etc in past 17 hours - think 12 to 16," he tweeted.

Reuters was eventually allowed to continue reporting with a police escort provided for security reasons.

An interior ministry official later told Reuters the situation had been the result of a misunderstanding by over-enthusiastic local police.

"This is not our policy. We have nothing to hide, and we want to facilitate journalists," the official, who did not wish to be named, said.

Several security officials said the restrictions on the press were partly due to Pakistani fears that the country would be blamed for Malik's actions.

"Pakistan has nothing to do with this but it will be used to malign Pakistan. So of course we have to care about how this is being seen and reported," one official said.

On Sunday, Interior Minister Chaudhry Nisar said Pakistan was willing to give any assistance that the United States required to investigate Malik, and highlighted that she spent most of her life in Saudi Arabia.

"Such acts of terrorism which take place across the world bring a bad name to Islam," he said. "You cannot blame the religion and the nation due to the personal actions of one person."