DAMASCUS (AFP) - Thousands of Syrian troops backed by tanks stormed the flashpoint town of Daraa on Monday killing at least 25 people, witnesses said, as a leading rights activist accused Damascus of opting for a "military solution" to crush dissent. Troops also launched assaults on the Damascus suburbs of Douma and Al-Maadamiyeh, witnesses said, as the head of the UN human rights agency slammed what she called the security forces' disregard for human life. The US, which has repeatedly denounced Syria's repression of the protests, was considering sanctions against Damascus, an official in Washington said. Amman said Syria on Monday closed its border with Jordan in a statement quickly denied by Syrian customs chief Mustapha Bukai. Activist Abdullah Abazid told AFP by telephone from Daraa that Syrian forces were pounding the southern town near the border with heavy artillery and that "at least 25 martyrs have fallen." "There are still bodies sprawled in the streets," he said, with the sound of loud explosions and gunfire in the background. A group of activists said in a statement to media that "more than 25 people fell but no one could reach them because of the heavy shelling" and that only seven bodies were retrieved. They were identified by name and included a father and his two sons, said the statement which accused Syrian troops of firing indiscriminately with anti-aircraft guns. "The commander of the Third Army Corps, Kamal Ayyash, a citizen of Daraa , was arrested because he protested against the killings," the statement said. A resident earlier said he witnessed five people killed when their car was raked with fire in Daraa . Abazid said Daraa was "like being in a battlefield." The army seized at least two mosques in the town as well as the cemetery where scores of people killed in anti-regime protests have been buried, activists said. The assault began at dawn when 3,000 to 5,000 army and security forces swooped down on Daraa , with tanks taking up position in the town centre and snipers deploying on rooftops, activists said. "The minarets of the mosques are appealing for help. The security forces are entering houses. There is a curfew and they fire on those who leave their homes. They even shot at water tanks on roofs to deprive people of water," said a witness. A massive crackdown was also under way in Douma, a large suburb in northern Damascus, and nearby Al-Maadamiyeh, said activists reached by telephone. In Washington, US National Security Council spokesman Tommy Vietor said his government could respond to the "brutal violence" with sanctions. "The United States is pursuing a range of possible policy options, including targeted sanctions, to respond to the crackdown and make clear that this behaviour is unacceptable," said Vietor. "The Syrian people's call for freedom of expression, association, peaceful assembly, and the ability to freely choose their leaders must be heard." UN High Commissioner for Human Rights Navi Pillay said the killings must stop. "Just a few days after the announcement of sweeping and important reforms, we are seeing such disregard for human life by Syrian security forces," she said in a statement issued in Geneva. Meanwhile diplomats said that Britain, France, Germany and Portugal are seeking a UN Security Council condemnation of the killing of demonstrators in Syria and a call for an independent investigation.