Somalia's Islamists vowed a "holy war" on Thursday (July 20) against Ethiopian troops crossing into the Horn of Africa nation, while Addis Ababa threatened to "crush" any attack on the interim government it supports. The aggressive rhetoric -- combined with this week's military moves on both sides -- have heightened fears of a new war in Somalia, plagued by violence and without central rule since the 1991 deposing of a military dictator. John Prendergast, of the International Crisis Group think-tank, said the risk of full scale war was increasing by the day. Islamists took the capital Mogadishu from US-backed warlords last month and are threatening the authority of a transitional administration formed in Kenya in 2004 and intended to steer the nation from anarchy to peace. Sheikh Mukhtar Robow, a senior Islamist in charge of defence, said around 20 military vehicles from Ethiopia had crossed into Somalia at Dollow on Wednesday (July 19). That added to previous Islamist accusations Ethiopia was pouring in troops to support Somalia's government against them. Independent analysts believe Addis Ababa has sent up to 5,000 troops into Somalia, and is massing many more on the border, as a deterrent to any more advances by the Islamists, who took Mogadishu from US-backed warlords last month. The regional power, Ethiopia backs the interim government of President Abdullahi Yusuf, based in the provincial town of Baidoa because it lacks the strength to move into Mogadishu. Ethiopia denied incursions into Somalia but threatened to "crush" any bid by the Islamists to take Baidoa or cross the border. Nominally Christian-led Ethiopia, which condemns the Islamist leaders as "terrorists", is fearful of having a hardline Muslim state on its doorstep. It is also anxious at possible Islamist aspirations to establish a "Greater Somalia" which would incorporate areas inhabited by ethnic Somalis such as Ethiopia's Ogaden. Ethiopia sounded the alarm after Islamist militia moved from Mogadishu to Buur Hakaba -- just 60 km (37 miles) from Baidoa -- on Wednesday. The Islamists returned in the evening, saying they went to collect 150 soldiers switching sides from Yusuf's force. The soldiers carried new AK-47 rifles. One of the militiamen, Mohammed Ahmed Sonkor, described why he switched sides. "My name is Mohamed Ahmed Sonkor, they recruited me in the Hiran region, then they transferred me to Baidoa, we were committed to work for the Somali government and the Somalis, but later Abdullahi Yusuf decided to bring us Ethiopian troops," he said. Commander of the Islamic Court of Bay region, Shekh Mukhtar Hassan said they could have attacked Baidoa but chose not to. "Yesterday my aim wasn't to attack Baidoa, but I could, I respect the ongoing dialogue between the TFG (Transitional Federal Government) and Islamic courts in Sudan, and we hope it will be fruitful and lead to reconciliation." He was referring to stalled Arab League-brokered talks between the Islamists and government in Khartoum. The government pulled out of the last round, saying the Islamists broke an accord to stop military advances.