A high-ranking member of Syria's government has resigned his post and joined the opposition against President Bashar al-Assad.

Deputy oil minister Abdo Hussameddin, the highest-ranking official to defect so far, announced Wednesday in a YouTube video that he was joining the revolution of this dignified people.

The move came as visiting United Nations humanitarian-affairs chief Valerie Amos said the rebel stronghold Baba Amr, in the Syrian city of Homs, had been devastated.

I, Abdo Hussameddin, deputy oil and mineral wealth minister in Syria, announce my defection from the regime, resignation from my position and withdrawal from the Baath Party, Hussameddin said in the video.

I am joining the revolution of the people who reject injustice and the brutal campaign of the regime, he added. I tell the regime, which claims to own the country, 'You have nothing but the footprint of the tank driven by your barbarism to kill innocent people.'

Opposition members had helped arrange Hussameddin's resignation, Agence France-Presse reported.

According to experts, the high-level departure could be a sign that Assad's regime is starting to crack.

Until now, the regime's inner circle has remained loyal, in contrast to what happened in Tunisia, Egypt and Libya during uprisings last year.

Wednesday's visit to Baba Amr by U.N. official Amos was the first by an outside observer since the Syrian army launched a ground offensive to clear the urban district of opposition fighters a week ago.

Since then, pro-Assad military forces have kept the area sealed, claiming the operation was still underway.

But rebels accuse the regime of trying to hide evidence of summary executions and other atrocities committed by the army after escalating its month-old crackdown on anti-Assad demonstrators.

They haven't let anyone in for a week, and now they are going to let them in? the Associated Press quoted Homs activist Tarek Badrakhan as saying.