Correspondent in oil-rich Basra province saw protesters block access routes to the ports of Khor al-Zubair and Umm Qasr, as well as Rumailah oil field.

Trucks waiting to load up goods from the ports could be seen waiting empty behind crowds of demonstrators.

Khor al-Zubair is used for some heavy crude exports but also to import fuel products like benzene, while Umm Qasr is the main entry point for food and medicine into Iraq.

"Export and import activities have stopped because trucks cannot enter Khor al-Zubair or Umm Qasr ports," one official at Basra's port authority said.

A second official later said the route to Khor al-Zubair had been reopened but Umm Qasr remained shut.

Sit-ins have become a go-to tactic for Iraqis demonstrating against their government since early October.

In recent weeks, protesters have shut the road to Umm Qasr several times, causing a delay in offloading operations that on one occasion forced around a dozen ships to unload their cargo in another country.

Road closures have also impacted heavy crude from the Qayyarah field in northern Iraq from reaching Khor al-Zubair since earlier this month.

The prime minister's office has warned security forces "will not allow" protesters near key infrastructure, and riot police have forced roads open in deadly crackdowns.

More than 330 people have been killed since protests erupted on October 1 in Baghdad and across the south.

In the capital's main protest camp of Tahrir (Liberation) Square, thousands gathered Wednesday to express their ongoing frustration with the government's proposed reform measures.

Parliament met on Tuesday night to discuss a new electoral law and welfare changes, but the protesters -- most of them students -- turned out in even larger numbers the next day.

"Last night's session serves their own interests, not those of the people," said Younes, a 28-year-old protester.

Crowds have spilled over from Tahrir onto three main bridges that lead to the western bank of the Tigris, where key government buildings and embassies are based.

Overnight, they tried to cross two of the bridges to reach the so-called Green Zone but security forces deployed on the bridges fired tear gas to keep them back, a security source told AFP.