Five of Gaddafi's generals are among latest defectors to rebels as South African president seeks to broker ceasefire

Armed westerners have been filmed on the front line with rebels near Misrata in the first apparent confirmation that foreign special forces are playing an active role in the Libyan conflict.

A group of six westerners are clearly visible in a report by al-Jazeera from Dafniya, described as the westernmost point of the rebel lines west of the town of Misrata. Five of them were armed and wearing sand-coloured clothes, peaked caps, and cotton Arab scarves.

The sixth, apparently the most senior of the group, was carrying no visible weapon and wore a pink, short-sleeve shirt. He may be an intelligence officer. The group is seen talking to rebels and then quickly leaving on being spotted by the television crew.

The footage emerged as South Africa's president, Jacob Zuma, arrived in Tripoli in an attempt to broker a ceasefire. He described reports that he would ask Muammar Gaddafi to step down as "misleading", and said he would instead focus on humanitarian measures and ways to implement a plan concocted by the African Union for Libya make a transition to democratic rule but not seek Gaddafi's exile.

The westerners were seen by al-Jazeera on rebel lines late last week, days before British and French attack helicopters are due to join the Nato campaign. They are likely to be deployed on the outskirts of Misrata, from where pro-Gaddafi forces continue to shell rebel positions to the east.

There have been numerous reports in the British press that SAS soldiers are acting as spotters in Libya to help Nato warplanes target pro-Gaddafi forces. In March, six special forces soldiers and two MI6 officers were detained by rebel fighters when they landed on an abortive mission to meet rebel leaders in Benghazi, in an embarrassing episode for the SAS.

The group was withdrawn soon afterwards and a new "liaison team" sent in its place. Asked for comment on Monday, a Ministry of Defence spokeswoman said: "We don't have any forces out there."

The subject is sensitive as the UN security council resolution in March authorising the use of force in Libya specifically excludes "a foreign occupation force of any form on any part of Libyan territory".

Despite more than two months of bombing by Nato, rebels have remained unable to advance west of Misrata, or west of Brega, 300 miles to the east. The capital, Tripoli, also remains in the grip of Gaddafi, who has defied all attempts to force him to leave.

However, a fresh blow to his position came yesterday as eight Libyan army officers appeared in Rome, saying they were part of a group of as many as 120 military officials and soldiers who had defected from Gaddafi's side in recent days.

The eight officers – five generals, two colonels and a major – spoke at a news conference organised by the Italian government. The officers said they had defected in protest at Gaddafi's actions against his own people, citing killings of civilians and violence against women. They claimed that Gaddafi's campaign against the rebels was rapidly weakening.

Air force pilots landed in Italy and defected earlier in the rebellion. Under-trained and under-manned rebel forces have been encouraging defections as a way to whittle away support for Gaddafi in the absence of a ground army sent to assist them.

The latest group are reported to have been spurred largely by tensions arising from the appointment newcomers to senior positions in the security services.

The behaviour of these men, many of them relatively youthful Gaddafi loyalists in their mid-30s, are throught to have stirred anger and dismay among the army's officer ranks.

In April, William Hague announced that an expanded military liaison team would be dispatched to work with the Benghazi-based Transitional National Council, which is positioning itself as a democratic alternative to Gaddafi's rule.

The foreign secretary said the team would help the rebels improve "organisational structures, communications and logistics" but stressed: "Our officers will not be involved in training or arming the opposition's fighting forces, nor will they be involved in the planning or execution of the [transitional council's] military operations or in the provision of any other form of operational military advice."

There were unconfirmed reports at the time that Britain was planning to send former SAS members and other experienced soldiers to Libya under the cover of private security companies, paid for by Arab states, to train the anti-government forces.