Pakistani authorities widened their efforts to curb militant groups, including Lashkar-e-Taiba, the one suspected of conducting the Mumbai attacks, raiding some of their properties and arresting about 20 members, security officials said Tuesday. The Pakistani defense minister, Ahmad Mukhtar, on Tuesday told an Indian television channel, CNN-IBN, that Maulana Masood Azhar, the leader of another militant group, Jaish-e-Muhammad, had been placed under house arrest. Bush administration officials publicly praised the steps, which Secretary of State Condoleezza Rice and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, demanded during their visits to the region last week. "These are good and important steps and could potentially serve the cause of preventing further attacks," a State Department spokesman, Sean McCormack, told reporters in Washington. "That's the last thing that either side needs." But questions remained about how far the Pakistani government would rein in the groups, which have functioned as an arm of Pakistan's military and intelligence services for two decades. Details of exactly what the government had actually done so far remained unclear. Pakistan said Tuesday that it had arrested Zaki-ur-Rehman Lakhvi, the operational leader of Lashkar-e-Taiba, during a raid on Sunday on a camp outside Muzaffarabad, the capital of the Pakistani-controlled region of Kashmir. Mr. Lakhvi has been described as the mastermind of the Mumbai attacks. But a senior American official said there was no independent proof of his capture, and it was not clear whether the Lashkar members the Pakistanis said they had rounded up Monday at offices and camps were fighters or senior commanders. American counterterrorism officials in Washington privately struck a skeptical tone, saying that they wanted to see proof that Mr. Lakhvi was actually in custody and that the arrests and raids actually represented a firm commitment by the government to crack down on the groups. "In the past when they've promised to move against these guys, they'd pick up one or two of them and then several months later, they'd release them," said a senior American official who has dealt with Pakistani authorities for several years. "Based on past patterns, we shouldn't expect much of this," said the official, who spoke on the condition of anonymity because he was not authorized to comment publicly on the case. Administration officials said they were watching India's reaction to Pakistan's words and deeds to gauge whether the raids and arrests would ease tensions between the countries. "There's a practical part of this " will these arrests lead to preventing further attacks and bringing people to justice," one senior administration official said, "and there's a political dimension " to what extent does this lower tensions between the two countries." Pakistani officials have indicated in the past few days that there were no plans for a large-scale crackdown on Lashkar-e-Taiba, a group founded in the 1980s by the Pakistani Army to fight a proxy war against India in Kashmir.