US drones prowled the sky over Pakistan's South Waziristan on Wednesday, a day after one of the aircraft attacked a stronghold of Pakistani Taleban leader Baitullah Mehsud, killing about 70 militants. The US attack came as the Pakistani army is preparing an all-out assault on Al-Qaeda ally Mehsud, who has been accused of orchestrating a campaign of bombings in Pakistan, including the 2007 assassination of former prime minister Benazir Bhutto. The push into South Waziristan on the Afghan border looms as the army is finishing off an offensive in the Swat valley, northwest of Islamabad, launched after Taleban gains raised fears for nuclear-armed Pakistan's future. US President Barack Obama's national security adviser, Jim Jones, arrived in Pakistan on a trip that includes stops in Afghanistan and India aimed at following up on the implementation of a new US strategy for the region. He will meet civilian and military leaders, a spokesman said. The pilotless US drone strike late on Tuesday, on a funeral for one of six militants killed in a similar strike earlier in the day, suggests closer coordination between the US and Pakistan. But Pakistan, which officially objects to such strikes, is unlikely to confirm that in a country where many people are suspicious of the alliance with the United States in its global campaign against militancy. Intelligence officials said late on Tuesday 45 people had been killed in the drone attack as mourners were leaving the funeral. On Wednesday, they said about 70 people had been killed. A Taleban official said Mehsud had been in the area but was not hurt. Security officials and villagers said the Taleban had sealed off the site. “Bodies are still lying there and the Taleban are not allowing anybody close while their men are coming and going in vehicles,” resident Ghulam Rasool told Reuters by telephone. Taleban spokesman Wali-ur-Rehman said 65 people had been killed and many would be buried in mass graves. “Most of the bodies are charred beyond recognition so it's been decided they'll be buried in three graves,” he said. On Wednesday, the militants fired at US drones flying over the remote, mountainous region and at least two turned back, said another resident. Taleban claim killing rival The military has been launching airstrikes on Mehsud's bases for more than a week while soldiers have been securing main roads into the region, sealing off his stronghold. A military convoy, including tanks and armoured personnel carriers, headed towards the area on Wednesday, a Reuters reporter in the region said. Tuesday's drone attacks happened hours after a gunman working as a guard killed a rival of Mehsud who had spoken out strongly against the Taleban chief. Rehman said the Taleban had killed the rival militant leader, Qari Zainuddin, and warned others not to support the government. “Whoever extends a hand of support to the government will be targeted the same way,” he said. The killing of Zainuddin, in the North West Frontier town of Dera Ismail Khan, showed Mehsud's reach and would be a setback for government efforts to win over ethnic Pashtun tribal factions for the campaign against Mehsud, analysts said.