Saudi Arabia has announced the assembly of a “massive” force on its border with Yemen, ahead of a proposed 5-day ceasefire to start on Tuesday.

The Saudi Defense Ministry issued a statement on the deployment, after Saudi forces traded artillery and rocket fire on Monday with fighters of Yemen’s ruling Ansar Allah (Houthi) movement. Footage on Saudi-owned TV showed rows of tanks and armored personnel carriers, loaded on military vehicles, moving towards the border.

On Sunday, Ansar Allah — which claimed power in the Yemeni capital Sana’a in February, a month before a Saudi-led coalition began aerial attacks — said it would accept the ceasefire proposed by the US and Saudi Arabia to allow humanitarian aid to reach Yemenis.

Saudi Arabia said the halt in fighting would proceed provided Ansar Allah did not try to advance on the ground, including its push to take areas of southern Yemen.

On Monday, Saudi forces reportedly hit Saada and Hajjah Province in northern Yemen — the long-time bases of Ansar Allah — with 150 rockets. Ansar Allah responded with Katyusha rockets and mortars on the Saudi cities of Jizan and Najran.

Saudi Arabia’s civil defence department said one Saudi national was killed in the shelling of Najran, with another Saudi citizen and three expatriates injured.

Saudi-led coalition jets bombed Ansar Allah positions in the central city of Taiz and in the oil-producing Marib Province east of Sana’a. There were no immediate details on casualties.

More than 600 people have been killed, 1,300 wounded, and 300,000 displaced since the Saudis began bombing in late March.