Yemen's government said Friday it will join UN-mediated peace talks next week, as rocket fire from Iran-backed rebels reportedly killed 20 civilians and wounded dozens more in a busy market.
Meanwhile, the Saudi-led coalition sent new reinforcements over the border into Yemen in preparation for an offensive to retake the capital, seized by the Shiite Huthi insurgents a year ago.
And, in an ongoing campaign to soften up Sanaa, coalition warplanes struck an arms depot, triggering powerful explosions that killed at least seven civilians and wounded 10, witnesses and medics said.
International rights groups have repeatedly voiced alarm at the heavy civilian toll in the conflict, which the United Nations estimates has killed more than 4,500 people since March.
An AFP reporter at the Wadia border crossing from Saudi Arabia saw at least 40 vehicles cross into Yemen's oil-rich Marib province in part of the operation to recapture more territory from the Huthis, who swept southwards after taking Sanaa.
Since July, loyalists have recaptured the main port of Aden and four other southern provinces.
The vehicles were carrying Yemeni troops trained in Saudi Arabia as well as coalition soldiers whose nationality military officials declined to give.
Their arrival came as warplanes killed seven rebels in the eastern province of Marib, while other raids struck insurgent positions in neighbouring Shabwa province, military sources said.
Hours later, the rebels fired Katyusha rockets at the government headquarters in Marib's provincial capital, witnesses said.
But several rockets struck an adjacent market, killing at least 20 civilians and wounding dozens, medics and witnesses said.
Friday's violence came as the government confirmed it had agreed to take part in UN-mediated peace talks, which it said would be held in Oman next week.
Late Thursday, the UN special envoy for Yemen, Ismail Ould Cheikh Ahmed, said the exiled government and rebels had agreed to take part in peace talks in the region.
However, in the absence of any announcement from the rebels, government spokesman Rajih Badi was unsure they would attend.
The talks "may not take place," he told AFP.
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Oman, the only Gulf Cooperation Council member not taking part in the coalition, had hosted talks between the rebels and a US delegation before ultimately fruitless UN-brokered negotiations were held in Geneva in June.
It is also the only GCC member that has always maintained good relations with Iran.
The government of President Abedrabbo Mansour Hadi insisted that a rebel pullback from areas seized since last year -- as outlined by UN Resolution 2216 -- remained a precondition for negotiations.
- 'Large-scale operation' -
The Saudi-led coalition has waged daily air strikes against the rebels, who are backed by troops loyal to former president Ali Abdullah Saleh.
The coalition has intensified raids against rebels since last week, when a missile attack killed 60 Gulf troops, most of them Emiratis, in Marib province.
In preparation for a push on Sanaa, coalition member states have reportedly sent thousands of heavily armed reinforcements to Yemen since last week, mainly to Marib.
The government has also announced that 10,000 Yemenis are now ready to serve in a "national army being prepared to liberate Sanaa and other provinces".
"Preparations are ongoing for large-scale military operations to liberate the provinces of Marib and Jawf (in the north) in order to enter Sanaa," one of the Yemeni military officials told AFP.
The deputy head of the National Centre for Strategic Studies, Major General Thabet Hussein Saleh, told AFP the coalition had intensified its operations as a "preemptive measure" ahead of any "results that could come out of political talks."
He said he expected the "war scenario" to overpower any political talks, highlighting the importance of Marib in recapturing Sanaa.
"Marib is strategically important for Sanaa."
Loyalists "have a strong presence there" and being a vast desert made it an easier option than mountainous Taez -- which was also farther away from the capital.
"The resistance in the north (where the rebels have more popular support) is weaker than that of the south," said Saleh. "But Marib will become the first province to fall" in northern Yemen.