He said: "Obama is sending more troops to Afghanistan and that means more Americans will die. With just a handful of resources we can cause them even more casualties and deaths."
The commander claimed that foreign forces, not the Taliban, were responsible for most Afghan civilian deaths, but the opposite is true, the BBC's Ian Pannell in Kabul says.
Mr Obama reached his deployment decision after more than three months of deliberations and 10 top-level meetings with advisers.
In his speech at the West Point military academy in New York, he said US forces lacked "the full support they need to effectively train and partner with Afghan security forces and better secure the population".
"I have determined that it is in our vital national interest to send an additional 30,000 US troops to Afghanistan," he told cadets.
"After 18 months, our troops will begin to come home."
Rising violence - more than 900 US soldiers have died in Afghanistan - and August's discredited elections in the country have fanned domestic opposition to the eight-year-old war.
Mr Obama's top team have been on Capitol Hill trying to convince the serious and senior elected politicians that this is the right strategy
Gen Stanley McChrystal, the US commander in Afghanistan, who had asked for 40,000 extra troops, welcomed Mr Obama's speech, saying he had been given "a clear military mission" and the necessary resources.
The reinforcements will take the total number of US troops in Afghanistan to more than 100,000.
The BBC's Aleem Maqbool in Kandahar says that Gen McChrystal's message is that the president's announcement is not just about troop numbers but about a new clarity in the US mission there.
He told troops that the success of their operation would be judged not on how many militants were killed but how many Afghans were given new opportunities and gave up their support for the insurgency, our correspondent says.
Gen McChrystal also backed Mr Obama's estimate that enough progress would have been made by 2011 for the withdrawal of American forces to begin, although he warned of further casualties to come.
Other Nato member countries have been urged to send more troops
Some 32,000 other foreign troops are also serving in Afghanistan. Nato Secretary General Anders Fogh Rasmussen urged members to do more.
He told reporters on Wednesday that 5,000 extra troops would be sent in 2010, and "probably" a few thousand in addition.
"This is our fight together," he said. "We must finish it together."
The UN envoy to Afghanistan, Kai Eide, told the BBC he did not believe the announcement from Washington amounted to an exit strategy because a long-term commitment remained.
He stressed the need to strengthen Afghan institutions at a local level and build a sustainable economy.
The Afghan government said it supported the new US strategy.
Foreign Minister Rangin Dadfar Spanta said that with international help, Afghanistan's armed forces would be able to start taking responsibility for security in 18 months.
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