BEIRUT, Dec 28, Reuters - - Arab League monitors in Syria faced angry crowds, gunfire and explosions during their second visit to Homs, the heart of a nine-month revolt against President Bashar al-Assad, online videos appeared to show on Wednesday.

Activists uploaded footage on the Internet showing crowds surrounding a monitoring team's car on Wednesday shouting those who kill their people are traitors. In another video, orange-vested monitors rushed behind a concrete building amid heavy shooting and blasts.

The pictures were impossible to verify and most foreign journalists are banned from working in Syria.

The Arab League observers are in Syria to determine if Assad is keeping his promise to push through a peace plan and end his crackdown on the revolt that has pushed the country towards civil war.

Homs has been mired in violence during the uprising. City neighbourhoods have been pounded with army tank fire and mortar rounds in recent months. Armed clashes have increasingly overshadowed the peaceful protests that began in March.

The head of the Arab League mission earlier said he saw nothing frightening on his first trip to Homs on Tuesday. But France called the comment from Sudanese General Mustafa Dabi premature and urged Syria to give his team full access.

When you were in Homs yesterday 15 people died. We're not benefitting from your presence, one activist, named as Khaled Abu Salah, shouted at the mission in a video of its second trip on Wednesday in the Homs neighbourhood of Baba Amr.

The Arab League has said the mission needs about a week to determine whether Assad has stuck to his promise to withdraw tanks and troops, free prisoners and start a dialogue with the opposition.

General Dabi earlier called on activists to give his team more time.

Remember, this was only the first day and it will need investigation. We have 20 people who will be there for a long time, Dabi told Reuters, speaking from Damascus.

Washington also urged patience. It was just Day One, State Department spokesman Mark Toner said. We need to let this mission get up and running. Let them do their job and then let them give their judgement.

Assad has warned against foreign intervention which he says could spark a regional crisis. Assad says Syria is fighting foreign-backed Islamist terrorists who have killed more than 2,000 of its security forces.

State television on Wednesday said Damascus had freed 755 people detained in the unrest whose hands were not stained with Syrian blood. Thousands remain in detention.

U.S.-based Human Rights Watch accused Syrian authorities of transferring hundreds of detainees to military sites off-limits to Arab League monitors and urged the observers to insist on full access to all sites used for detention.

Unobstructed access and uncensored testimony are crucial to the Arab League's mission. The monitors hit a snag on Wednesday when locals in Baba Amr refused to speak with the observers in the presence of a Syrian army colonel.

The monitors later returned unescorted but had to scrap an effort to check an area where residents believed detainees were being hidden, because gunfire erupted nearby, activists told Reuters by telephone.

CLASHES RISE AHEAD OF MONITORS

As the monitors toured Homs, other hotspots saw fresh violence, said witnesses and activists.

A video sent by rebels in Deraa province showed gunmen with faces swathed in checkered kerchiefs, firing automatic rifles at a convoy of security force buses. The Syrian Observatory for Human Rights said four government soldiers died in the ambush.

Security forces fired live ammunition and tear gas at an anti-Assad rally in Hama, another major flashpoint of unrest north of Homs, said activists. At least one person died and seven were wounded, they added.

Al Jazeera television showed gunfire, curls of black smoke and men marching down a street chanting, Where are the Arab monitors? One man was bleeding from the neck.

The delegation plans to send teams to central Hama, southern Deraa and northern Idlib on Thursday.

Despite the hitches, many Homs residents were pleased with what they said was a more diligent second tour by monitors, and relieved to have a respite from days of heavy gun battles.

This has been less killing and shooting than usual so I'm feeling more relaxed, joked activist Mohammed Saleh.

In other video clips of the monitoring mission, observers scribbled notes as residents named missing loved ones and showed the team the body of a lifeless young boy shot in the back. The Syrian Observatory for Human Rights says three people died from gunshots in Homs on Wednesday.

RUSSIA PRODS ASSAD TO OPEN UP

Russia, one of Assad's few remaining allies and Syria's primary weapons supplier, urged Damascus to let the observers move around the country freely.

The mission should be able to visit any part of the country, any towns or villages, and come up with its own independent, objective opinion about what is happening and where, Foreign Minister Sergei Lavrov said.

Activists say about a third of the estimated 5,000 people killed in unrest in Syria since March died in Homs. Dozens have been killed in the past week alone and thousands arrested in the months before the 22-state Arab League was invited in.

The monitors represent the first international intervention on the ground in Syria since the revolt began. Protesters hope their final report will nudge the world into action against Assad.

(Additional reporting by Ayman Samir; Writing by Erika Solomon; Editing by Douglas Hamilton and Andrew Heavens)