JEDDAH, Saudi Arabia (Reuters) - Thousands of students at an all-female university in Saudi Arabia boycotted classes on Saturday, protesting against poor services, witnesses said, in a rare display of dissent from women in the conservative Islamic kingdom.

It was the second protest at King Khalid university in the southern town of Abha in a week - security forces broke up a demonstration there on Wednesday, leaving dozens injured, students told Reuters.

The protests first erupted when the university cancelled cleaning services, saying students needed to take better care of their campus.

"The main trigger was the accumulation of trash for three days which started to smell. The other thing is the mistreatment of students," one of the students told Reuters on Saturday, asking not to be named.

"Today there was a high rate of absences ... There were security and religious police outside the university but no arrests were made," the student added

Video footage posted on YouTube on Saturday appeared to show about 200 students at Abha's affiliated all-male King Khalid University also holding a protest against poor services and calling for the removal of the university's president.

Abdel Karim al-Hunaini, deputy governor of the surrounding Aseer province, told Reuters he thought the students at both establishments had a right to protest and local authorities would set up a committee to address their demands.

Saudi Arabia is investing heavily in education to deal with high youth unemployment in a country where about 70 percent of the native population of 19 million is under 30.

(Reporting by Asma Alsharif)