The U.N. World Food Programme began distributing food to around 340,000 people in the southern Yemeni port city of Aden, the agency said Thursday. "We are challenging the odds to reach tens of thousands of people who would go hungry without food assistance," Muhannad Hadi, regional director for the agency, said. "We are working to overcome insecurity, checkpoints and many other hurdles in Yemen to reach desperate families unable to feed their children," he added.

Nearly 4,000 people have been killed in Yemen in a conflict that escalated in mid-March, according to the U.N. The New York-based body said that around 21 million people, 80 percent of the population, are in need of assistance and among them, 13 million are food insecure. Humanitarian workers began distributing two-month food rations – including wheat flour, pulses and cooking oil – in a number of areas in Aden that had not been reached since April because of the conflict, the food agency said. On Saturday, the Saudi-led coalition, which has conducted four months of airstrikes against Iranian-backed Shiite Houthi rebel positions, called for a five-day humanitarian cease-fire to allow aid to flow into the impoverished country.

However, attacks by both sides have reportedly continued despite the truce. U.N. spokesman Stephane Dujarric on Thursday urged the parties to respect the cease-fire so that desperately needed humanitarian aid could reach civilians. "Every day underscores the need for the political discussions to get back on track, and most immediately, for all the players involved, all those who control the weapons, to silence them so we can get the humanitarian aid to where it needs to be," he told reporters. Yemen descended into chaos last September, when the Houthi rebels overran the capital, Sanaa. The move prompted a Saudi-led coalition to launch a military offensive in late March against the group.

Meanwhile, the Saudi led-coalition fighting to reinstate Yemen's exiled government aims first to reestablish it in the mostly recaptured port city of Aden and then return it to Sanaa if possible through peace talks with the Houthis, a coalition spokesman said on Thursday. But if the Houthis did not eventually agree to quit Sanaa, the government would have the right to "get them out" by force, Brig. Gen. Ahmed Asseri said in an interview. A Saudi-led Arab coalition allied with southern Yemeni fighters retook much of Aden last week in the first significant ground victory of their campaign to end Houthi control over much of the country and restore the exiled president, Abd Rabbuh Mansur Hadi. Yemeni forces backed by Saudi-led airstrikes have recaptured positions on Aden's outskirts used by Houthis to fire rockets into the city, local officials said on Thursday. Senior members of Yemen's exiled administration flew into Aden on July 16 to make preparations for the government's return to the major southern port, four months after it was pushed out by Houthi forces, the dominant armed faction in the conflict. Asseri, whose side has been conducting air raids on the Houthis since March 26, said the first task was to secure Aden so the government could operate from there for the moment.

"Aden was the first step. Now the government will start rebuilding their military capability, their security capability, the stability in cities," he said, and this would need time. "We believe that going surely, step-by-step, if the Houthis get out of Sanaa through peace talks, then this is important. "But if they keep controlling [Sanaa], I think the legitimate government has the right to get them out of Sanaa," which is in northern Yemen and has been frequently bombed by Saudi-led warplanes over the past four months.

Asseri said the Houthis ought to implement U.N. Security Council Resolution 2216, which calls for the Zaydi Shiite movement to withdraw from cities under their control, return seized arms and allow Hadi to return from his Riyadh exile. The Houthis have rejected that resolution, arguing they are pursuing a revolution against a corrupt government and they deny having any military or economic links to Shiite Iran, the Saudis' main regional foe. Asseri said the coalition welcomed investigators to Yemen to look into rights abuses by any side in the four-month-old war. "I assure you the coalition is very ready to cooperate with any investigation in Yemen," he said, stressing that it would be up to the Yemeni government to grant access to the country. Human Rights Watch has accused both sides of abuses, most recently the coalition over the July 24 raid in western Yemen and pro-Houthi rebels of firing rockets indiscriminately into residential areas in Aden.