Demonstrations have been held across Mexico as President Enrique Pena Nieto marked two years in office with his lowest approval rating yet.

Thousands marched on Monday through Mexico City, denouncing the president's handling of the case of 43 missing students, now presumed dead.

Protesters chanted for Nieto to resign while they waved blackened flags of the country.They echoed "you are not alone" to parents of the missing students who joined the protest.

The protests were largely peaceful, but turned violent at some places at night.

Al Jazeera's Monica Villamizar, reporting from the capital, said fires were lit, windows smashed and banks vandalised. She said there was a small confrontation between protesters and police and a large presence of anti-riot police.

We no longer recognise Enrique Pena Nieto as president of Mexico because he has not met our central demand, which is to present our sons alive. Felipe de la Cruz, spokesperson for families of the missing students

Thousands also protested in the southern state of Guerrero, where a drug gang confessed to killing 43 college students after local police handed them over in September.

A group of protesters ransacked the Guerrero state prosecutor's office in the regional capital, Chilpancingo, and set five vehicles on fire, including two police cruisers.

Other protesters led by a teachers' union have also blockaded a state-owned oil refinery in southern Mexico.

"We no longer recognise Enrique Pena Nieto as president of Mexico because he has not met our central demand, which is to present our sons alive," Felipe de la Cruz, a spokesman for the families of the missing, told the AFP news agency.

Families refuse to believe the 43 young men are dead and demand they are found alive. Federal prosecutors have stopped short of declaring them dead, saying they await DNA tests on charred remains sent to an Austrian university.

'Mexican awakening'

The case has put a spotlight on Mexico's struggle to end corruption and impunity amid a drug war that has left 100,000 people dead or missing since 2006.

"This is what people are calling the Mexican awakening," said our correspondent. "Protests have been going on for more than two months.

"People are telling me they want the president to step down. They asked for reform and he announced reforms but they say that is not enough."

A poll published by El Universal newspaper showed that 41 percent of Mexicans approve of Nieto's performance while the daily Reforma found that 39 percent were satisfied.

It was the worst approval rating for a president since Ernesto Zedillo in the mid-1990s, underscoring the magnitude of the crisis Nieto is facing.