In a major battlefield success, Islamic militants attacked and occupied a Pakistani military fort on the Afghan border, officials said Wednesday. Seven Pakistani frontier guards died in the assault and 20 were listed as missing. Army spokesman Maj. Gen. Athar Abbas said 50 attackers died in the surprise attack on Sararogha Fort in South Waziristan on Tuesday night. The casualty figure could not be independently confirmed, and in the past the rebels have dismissed government claims about their losses as heavily inflated. "About 200 militants charged the fort from four sides," Abbas said. "They broke through the fort's wall with rockets." Fifteen members of the 42-man Frontier Constabulary garrison reached safety in Jandola, an army base about 35 kilometers (22 miles) east of the occupied British-era fort. Another 20 were still missing, Abbas said. The capture of Sararogha Fort represents the first time the militants have managed to isolate and capture a strongly defended government position since October, when they seized several isolated police stations and small military posts in Swat valley, another volatile region in the country's north. The government has since recaptured the valley. The attack comes as Pakistan is reeling from a series of suicide attacks in which about 400 people have perished. They include Benazir Bhutto, a former prime minister and leading opposition politician, who was assassinated on Dec. 27. The Pakistani army has deployed nearly 100,000 troops with heavy artillery and Cobra helicopter gunships to the border regions to try to block cross-border infiltration by Taliban militants fighting US and NATO forces in Afghanistan. US officials also fear al-Qaida has regrouped in the lawless tribal belt. Analysts said Wednesday's setback at Sararogha demonstrated that the government of President Pervez Musharraf was failing to contain a growing Islamist insurgency ahead of parliamentary elections scheduled for Feb. 18. "This is a huge loss," said Talat Masood, a retired general and now a political analyst. "The militants are now challenging the army openly. They have become very bold and are consolidating their positions." Local tribesmen were increasingly joining up with Taliban forces from across the border in Afghanistan, he said. "Even if they don't support Taliban per se, they are now siding with them rather than government because they think the Musharraf and the army are an extension of the Americans," Masood said. Washington considers Musharraf, who seized power in a military coup in 1999, a key ally in its war on terrorism. President George W. Bush and leading members of his administration have frequently praised Musharraf, who resigned from the army in December and is now ruling as a civilian president, for a commitment to democracy. Opposition leaders also were quick to blame Musharraf for the deteriorating security situation in the country. "Musharraf is the root cause of all problems," said Nawaz Sharif, a leading opposition politician and former prime minister who was overthrown by Musharraf in 1999. "If he goes, 95 percent of the problems of this country will be solved. There will be no bomb blasts, there will be no missile attacks," Sharif told journalists in his home town of Lahore. Meanwhile, Bhutto's political party said it sent a letter to the United Nations asking it to form a committee to investigate her Dec. 27 assassination. The party says it does not trust Musharraf's government to competently probe the killing. It is unlikely the United Nations will consider the request because it did not come from the government, which has said it will not seek the help of the world body.