The UN is preparing to impose sanctions on five prominent Yemenis, including Ali Abdullah Saleh, the former president, Al Jazeera has learned.

A UN panel of experts found that the individuals had been undermining Yemen's democratic transition.

Three of those named are leaders of the Houthi rebel group that has seized large parts of the country over the past month.

Saleh, whose 33-year reign ended in 2012 after a popular uprising, has been accused of using Yemen's ongoing crisis to re-establish his influence over the country's politics.

His powerful son Ahmed Ali, who was the brigadier-general in charge of the Republican Guard before he was named the ambassador to the UAE, is also to be sanctioned, Arab diplomats who have seen the report prepared by the UN panel told Al Jazeera.

The three Houthis listed are the group's leader Abdulmalik al-Houthi, his brother Abdulkhaleq al-Houthi and military leader Abu Ali al-Hakem.

Some Yemenis say there is a hidden alliance between the Houthis and Saleh, who belongs to the Shia Zaidi sect that the Houthis hail from.

Diplomatic immunity

Without the backing of Saleh, some observers say, the Houthis would not have been able to take the capital and other parts of the country.

The Houthis, who now control Sanaa and several other provinces, hail from the northern highlands and are increasingly imposing their authority outside the capital as well as in it.

Al Jazeera's Diplomatic Editor James Bays, speaking from the UN headquarters in New York City, said sanctioning Saleh's son would be controversial since he has diplomatic immunity as an ambassador.

He has said it would also be problematic to sanction the Houthi leaders, because they are so important, both politically and militarily.

"In the short term, it could make things worse rather than better," he said. "If you're trying to get any political reconciliation to happen, it will be important to have them on board."

The UN Security Council in February authorised sanctions against anyone in Yemen who obstructs the country's political transition or commits human rights violations but stopped short of blacklisting any specific individuals.

Al Jazeera's Bays said the UN Committee 2140 could decide on the sanctions as early as in the coming week.

Hakim al-Masmari, editor of the Yemen Post, says he is doubtful that Saleh and his son will be sanctioned since they are possibly the most powerful people in Yemen today.

Possible backlash

Since Saleh is still president of the influential General People's Congress party, which is united behind him, sanctioning him could lead to a backlash, Masmari told Al Jazeera.

"What this could mean is that half of the country's people could boycott the next government or go against the international community," he said.

Noting that the UN sanctions would also hit people with financial links to those blacklisted, Masmari said that in the case of Saleh and his son, "this could affect thousands of people, worth millions of dollars".

Sanctioning the Houthi leaders, on the other hand, would have no effect on the rebel group, he said.

"They don't have bank accounts, and they don't travel, so sanctions on them will have no influence in any way, at least in the next couple of years," Masmari said.

Meanwhile, on the ground in Yemen, renewed fighting between Houthis and Sunni tribesmen backed by al-Qaeda in the Arabian Peninsula (AQAP) has killed dozens of people.

Sources told Al Jazeera that 67 Houthis were killed in attacks as they advanced into Radaa - a mixed Sunni-Shia town that is an al-Qaeda stronghold.