Yemen’s Houthi fighters and Saudi Arabian forces have traded heavy artillery and rocket fire in border areas, residents say, a day before a proposed ceasefire.

The Houthis said they fired Katyusha rockets and mortars on the Saudi cities of Jizan and Najran on Monday, after the Saudis hit Saada and Hajjah provinces with more than 150 rockets, the Reuters news agency reported.

Saudi Arabia’s civil defence department said that one Saudi person was killed in the shelling in Najran, which it said targeted a school and residence adjacent to a military post.

Another Saudi national and three expatriates were also injured in the attacks, the department said.

Planes from a coalition led by Saudi Arabia also struck positions of the Houthis, believed to be backed by Iran, in the central city of Taiz and in the oil-producing Marib province east of the capital, Sanaa. There were no immediate details on any casualties.

The renewed border fighting came nearly a week after Houthis launched a mortar and rocket attack on Najran, reportedly killing several Saudis.

At the time, the Saudi government said the Houthis had crossed “a red line” by carrying out the attack.

Al Jazeera’s Mohammed Vall, reporting from Riyadh, said the Saudis had sent a “massive additional force” to the Yemeni border, following Monday’s exchange of fire.

“The Houthis have escalated their activities along the border and that has led to an intensification of air strikes in previous days,” he said.

More than six weeks of air strikes have failed to push back the Houthis and militia and army units loyal to the former president, Ali Abdullah Saleh.

Saleh on Sunday formally announced an alliance with Houthis after his house in Sanaa was bombed.

The rebels, whose ties to regional rival Iran has rattled the Gulf Arab states, remain the dominant political force in the impoverished Arab country that borders Saudi Arabia, the world’s top oil exporter.

Ceasefire flagged

Saudi Arabia has offered a five-day ceasefire starting on Tuesday evening to allow delivery of humanitarian supplies into the country, but warned that the truce depended on the Houthis abiding by that deal.

The Houthis’ political council has said that they would like to see humanitarian aid delivered to the Yemeni people as soon as possible.

Vall said instead of seeing a lessening of fighting as the proposed truce neared, “what we see is an escalation”.

A group of 17 international aid agencies said on Sunday that five days was not sufficient to provide relief to the country, which after weeks of an air and sea blockade is suffering severe food and medicine shortages.

Speaking to Al Jazeera from the Saudi capital Riyadh on Monday, however, Yemen’s Foreign Minister Riyad Yassin said he believed the Houthis had no desire for a ceasefire deal.

“The Houthis … they will not comply with any ceasefire and they are not willing to do any kind of discussion or negotiation,” Yassin said.

Meanwhile, the Moroccan Royal Armed Forces said in a statement on Monday that one of its F-16 fighter jets, taking part in the Yemen air raids had gone missing.

Al Jazeera’s Vall said the downing of the jet would further complicate the political situation with the proposed truce.

“We understand the Arab coalition is going to try to search on the ground to try to find the pilot if he’s still alive and probably try to rescue any debris they can from the aircraft,” Vall said.

“This is difficult because the aircraft came down in Saada. It is a mountainous area and very difficult to access for the coalition troops.”

Backed by the US, the coalition has been conducting air raids against the Houthi fighters since March 26, nearly a month after the rebels toppled the government of President Abd-Rabbu Mansour Hadi. Al Jazeera