Correction, 1/4/2015: An earlier version of this article said MSF had received more than 550 patients in Aden since March 19 "as a result of the Saudi-led bombing". The words "as a result of the Saudi-led bombing" were removed, because these were our words, not those of MSF. This was unclear from the way the sentence was written.

UN rights chief has said that Yemen is "on the verge of total collapse" as Saudi-led coalition continues to bomb Houthi positions.

"The situation in Yemen is extremely alarming, with dozens of civilians killed over the past four days," UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said on Tuesday.

"The country seems to be on the verge of total collapse".

Children are in desperate need of protection, and all parties to the conflict should do all in their power to keep children safe Julien Harneis, UNICEF

Aid groups have warned of a humanitarian crisis unfolding with air and sea blockades making it impossible to send desperately needed assistance as casualties mount.

The UN children's fund said that at least 62 children had been killed and 30 injured during the fighting over the past week.

"Children are in desperate need of protection, and all parties to the conflict should do all in their power to keep children safe," said UNICEF's Julien Harneis.

Doctors Without Borders (MSF) said it had received more than 550 patients in the southern city of Aden since March 19.

"We urgently need to find ways to get humanitarian relief and personnel inside the country," said MSF's Greg Elder.

Amnesty International accused the Saudi-led coalition of "turning a blind eye to civilian deaths" as it reported four children were among six burned to death in strikes on Ibb, in central Yemen.

The UN has also criticised the deadly bombing of a camp for displaced people in north Yemen, saying it was a violation of international law.

"We have not identified who is responsible for this attack," UN spokesman Farhan Haq said. "Whichever forces are hitting them are in violation of the law, there should be accountability for that and ultimately all such attacks have to cease."

UN Secretary General Ban Ki-moon separately said he was "deeply concerned" by reports of numerous civilian deaths from the military campaign against Shia Houthi rebels, who deposed internationally recognised President Abd-Rabbu Mansour Hadi in February.

Houthis advance

But the spokesman for the Saudi-led coalition said it does not intend to kill civilians even though the Houthis had moved fighters into villages.

"Collateral damage can happen... but I confirm to you that the coalition takes all care," said Brigadier General Ahmed Assiri.

On Tuesday, air strikes targeted two Houthi-held camps and Guard soldiers in the southern town of Daleh, a Guard airbase in the southwestern city of Taez and the Houthi stronghold of Dhammar, south of Sanaa.

On the ground, deadly clashes have broken out between the rebels and tribes, militiamen and residents who oppose their power grab, the AFP news agency reported.

Yemeni military officials said Houthi rebels have taken up positions overlooking the strategic Gulf of Aden, raising the risk they could threaten the global shipping route with heavy weapons, the AP news agency reported.

They say the rebels, which have been the target of a Saudi-led air offensive, are positioned in areas called Zabab and the Sheikh Said mountain next to the Bab-el-Mandeb strait.

They say Saudi warplanes had bombed nearby islands and that heavy anti-aircraft fire could be seen reaching upward into the sky on Tuesday night.

The strait leads from the Arabian Sea to Egypt's Suez Canal, a vital route for shipping between Europe and Asia.