Rebels in northern Yemen have said they shot down a Yemeni fighter jet that was attacking their strongholds on Sunday.
The government in Sanaa has denied the claim, saying the Sukhoi crashed because of a "technical error".
It was the third Yemeni military plane to crash since the latest fighting between the army and the rebels, known as the Houthis, began four months ago.
Earlier, Saudi Arabia said it had regained control of territory seized by the rebels in an incursion last week.
Saudi officials said the air and ground offensive, launched last week after a soldier was killed in a raid in the Jizan region, had not strayed into Yemen.
However, the Houthis, Yemeni officials and Arab diplomats said Saudi forces had repeatedly struck deep inside northern Yemen.
"The Saudi air raids resumed this morning," rebel spokesman Mohammed Abdul Salam told the AFP news agency on Monday.
"Saudi combat fighter jets launched intense raids against border areas inside Yemeni territory on Sunday night. The Saudi military used phosphorus bombs during those night raids, burning mountainous regions."
Mr Abdul Salam said the aircraft had targeted the region of Jabal al-Dukhan, the villages of Hassama and Shida, and the town of al-Malahit, which lies 7km (4 miles) inside Yemen, killing civilians.
He also denied that rebel fighters had crossed the Saudi border, saying those who had been detained were illegal migrants, and accused the Saudi government of allowing the Yemeni military to use its territory to launch attacks.
But Saudi Assistant Defence Minister Khaled Bin Sultan insisted on Sunday that Saudi troops were merely seeking to force the rebels from its territory and seal the border to prevent incursions.
Saudi television aired footage on Sunday of Saudi soldiers capturing and blindfolding men who were identified as Houthi fighters.
On Saturday, Yemeni President Ali Abdullah Saleh vowed to crush the rebels, and that there would be no let up in the battle "until we bring this tyrannical, traitorous and mercenary group to an end".
"The war just started two days ago, and what has been happening in the past six years was just... training for the army," he said. "The war will never stop no matter how much money or martyrs it costs."
The Houthis, named after the family of their leader, say they want greater autonomy and a greater role for their version of Shia Islam. They complain that their community is discriminated against.
They also accuse Saudi Arabia of supporting the Yemeni armed forces by allowing them to launch attacks from its territory, a charge which both countries deny.
The Yemeni government accuses the rebels of wanting to re-establish Zaydi Shia clerical rule, and of receiving support from Iran.
The Zaydi Shia community are a minority in Yemen, but make up the majority in the north of the country.
The insurgents first took up arms against the government in 2004, after which government forces killed or captured much of the Houthi leadership.
The government launched a fresh offensive in August 2009 which has precipitated a new wave of intense fighting.
Aid agencies say tens of thousands of people have been displaced.
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