Every day scores of Yemeni civilians straggle into this scorching, sandblown camp near the Saudi border, fleeing battles raging between the army and Shi'ite rebels in northern Yemen for the past two months.

"I arrived here with my family at the beginning of Ramadan (late August) after walking and hitch-hiking for two days," said Saleh Yahia al-Shanab, 29, from Aqarib, a village in the Malahit district on Yemen's northwestern border with Saudi Arabia.

"We left our belongings because all we cared for was the safety of our heads. Houthis deployed to our village overnight," he said, referring to the rebels led by Abdul-Malik al-Houthi.

"All of a sudden we heard their cries from every part of the village. They were shouting 'Death to America, Death to Israel."

UN agencies say about 150,000 Yemenis have been displaced since the conflict flared in 2004, but limited access to the war zone means they have no clear idea how many have fled their homes since the army's "Operation Scorched Earth" on Aug. 11.

Andrew Knight, a spokesman for the UN High Commissioner for Refugees, said 20 to 30 families a day were arriving in al-Mazraq camp, which already houses about 6,000 people.

Yemeni authorities have barred journalists and diplomats from travelling independently to the rugged provinces of Saada, Amran and Hajjeh, where troops and pro-government tribesmen are battling the well-armed Houthis and their tribal allies.

A senior UN official was due to start a four-day visit to Yemen on Thursday to try to draw attention to the plight of civilians affected by a war the world has largely ignored.

The United Nations said John Holmes, undersecretary-general for humanitarian affairs and emergency relief coordinator, "hopes to highlight the potential impact of continued neglect by the international community to humanitarian needs in Yemen".

Shortage of tents

Some of those needs are on stark display at al-Mazraq camp, 35 km (22 miles) northeast of the border post at Haradh.

"We are short of foodstuffs, latrines and especially tents," complained Abdu Sagheer, who had fled from the Haidan district.

"There is one tent with 12 families living in it. Some people have been here for 20 days and have yet to get tents."

Hundreds of men queue at midday outside a communal kitchen where they collect a meal of rice and meat for their families.

Women gather near white plastic tanks to collect water in 20-litre jerry cans. Some said the tanks emptied quickly, forcing them to wait hours until tanker trucks refilled them.

Sandstorms hit the area several times a day, blowing dust into the randomly erected tents that line the camp's main road, offering scant relief from the 43 degree (109 Fahrenheit) heat.

The nearby town of al-Mazraq is bustling with troops and armoured vehicles. At noon soldiers crowd the local market to buy bunches of qat, a mildly narcotic drug widely used in Yemen.

Pratibha Mehta, the United Nations resident coordinator in Yemen, said international relief agencies were providing assistance to about 75,000 displaced civilians, but in some cases only intermittently because of insecurity.

"We have challenges accessing all the IDPs (internally displaced people)," she told Reuters from Sanaa, adding that many people escaping the fighting had taken refuge with friends and relatives rather than in camps, which lack privacy.

A UN flash appeal for $23 million for Yemen launched at the beginning of September remains largely unfunded, Mehta said.

International aid agencies are liaising with a high-level government inter-ministerial relief committee, but some human rights groups have criticised the effort.

Human Rights Watch this week urged Yemeni authorities to allow aid agencies to help civilians trapped by the conflict.

"Fighting and government restrictions mean tens of thousand of civilians in northern Yemen are cut off from help that they desperately need," said Joe Stork, deputy Middle East director at the New York-based watchdog, in a statement on Monday.

The UN refugee agency has delayed an aid convoy that was due to set off from Saudi Arabia for Yemen this week.

A UNHCR official in Riyadh said the convoy, intended to help 2,000 people stranded near the border, was still waiting for security clearance from the Saudi and Yemeni sides. – Reuters