Syria's deputy oil minister resigned on Thursday, becoming the most senior official to join the rebel ranks, as Washington revealed it is mulling non-lethal aid to the insurgency.

Abdo Hussameddin announced his resignation in a video posted by activists on YouTube, saying he was joining the revolt.

"I, the engineer Abdo Hussameddin, the deputy oil minister... announce my defection from the regime and my resignation," he said in the video.

"I am joining the revolution of the people who reject injustice and the brutal campaign of the regime, which is seeking to crush the people's demand for freedom and dignity," he added.

The resigning minister said he had served in the Syrian government for 33 years and did not wish to end his life ‘serving a criminal regime’.

Hussameddin thus becomes the highest-ranking Syrian official to resign from the regime of Syrian President Bashar el-Assad, who has been battling a year-long revolt.

The news of the ministerial resignation came hours after US Defense Secretary Leon Panetta said Washington was looking at delivering non-lethal aid to Syria's rebels, hinting at the first direct US assistance to the forces seeking Assad's downfall.

While outraged at the killing of civilians in Syria, the US government is opposed to taking unilateral military action and favors pursuing diplomacy to force Assad to step down, Panetta told the Senate Armed Services Committee.

"We are reviewing all possible additional steps that can be taken with our international partners to support efforts to protect the Syrian people, end the violence and ensure regional stability, including potential military options if necessary," Panetta stressed.

Asked by Senator Richard Blumenthal if the United States was ready to deliver communications equipment to Syrian rebels, Panetta said: "I'd prefer to discuss that in a closed session but I can tell you that we're considering an array of non-lethal assistance."

His answer marked the first time President Barack Obama's administration had suggested it was ready to provide direct assistance to Syria's rebels, who are badly outgunned by the regime's tanks and artillery.

According to the United Nations, more than 7,500 people have died in the brutal government crackdown to put down the revolt that erupted last March.

On Wednesday, UN humanitarian chief Valerie Amos briefly visited the battered neighbourhood of Baba Amr, in the protest city of Homs, with a Syrian Red Crescent team.

However Amos was stopped from going into areas of Homs still held by the opposition, despite receiving assurances from Syrian Foreign Minister Walid Muallem in earlier talks that she could go to any part of the country, her spokeswoman Amanda Pitt said.

"She says that the parts they saw were completely devastated," Pitt said. "She said Homs feels like a city that has been completely closed down.

The Red Crescent and the International Committee of the Red Cross had been trying since last Friday to enter Baba Amr - the target of a month-long bombardment to oust rebel fighters - but the government repeatedly barred them from evacuating wounded civilians and delivering desperately needed supplies.

The Syrian Observatory for Human Rights said 27 people were killed in violence across Syria on Wednesday alone, 10 of them in the central Homs province.

In Hama province, also central, seven members of one family were said to have died during shooting and shelling in the town of Shayzar.

The London-based observatory said the death toll also included seven army defectors.

In his video comments, Hussameddin denounced Russia and China for backing the Syiran regime saying they were not "friends of the Syrian people but partners in the killing of the Syrian people".

He advised his colleagues to abandon ‘this sinking ship’.

Rami, the activist who shot the video of the defecting Hussameddin and posted it on YouTube, said in Beirut that the opposition helped arrange his resignation.

He asked that the location where the video was shot not be disclosed for safety reasons.

UN-Arab League envoy Kofi Annan is hoping to get the chance on Saturday to see how far the country has sunk.

The former UN chief was in Cairo on Wednesday ahead of his first visit since his appointment as international envoy for Syria.

Tunisian President Moncef Marzouki renewed an offer of asylum to Assad in an interview to be shown Thursday, after Russia said there was no question of it granting the Syrian leader refuge.

Meanwhile Russia's UN envoy on Wednesday accused Libya of helping to train Syrian rebels to carry out attacks on Damascus government targets.

"We have received information that there is in Libya, with the support of the authorities, a special training center for Syrian revolutionaries and these people are sent to Syria to attack the legal government," ambassador Vitaly Churkin said.