Yet to decide how many troops will be deployed to Afghanistan: US Defence Secretary James Mattis

The Pentagon has not decided yet how many more U.S. troops to send to Afghanistan, Defense Secretary James Mattis said on Tuesday, after President Donald Trump committed the United States to an open-ended war there.

Trump offered few specifics in a televised address about Afghanistan on Monday, but promised a stepped-up military campaign against Taliban insurgents who have gained ground against U.S.-backed Afghan government forces. He also singled out Pakistan for harbouring terrorists, an accusation denied by Islamabad.

The Afghan government welcomed Trump's speech but the Taliban said it would make the country a "graveyard for the American empire."

Mattis said he was waiting for a plan from the U.S. military's chairman of the Joint Chiefs of Staff, General Joseph Dunford, before deciding how many more troops to send to Afghanistan, where the United States is fighting its longest war.

"When he brings that to me, I will determine how many more we need to send in," Mattis told reporters during a visit to Baghdad. "It may or may not be the number that is bandied about."

U.S. officials have said Trump has given Mattis the authority to send about 4,000 additional troops to add to the roughly 8,400 already in Afghanistan.

Trump has previously called for a U.S. withdrawal from Afghanistan. On Monday he said his original instinct was to pull out all American troops but that he was convinced otherwise by his military advisers after a lengthy strategy review.

"The consequences of a rapid exit are both predictable and unacceptable," he said. "A hasty withdrawal would create a vacuum that terrorists, including ISIS (Islamic State) and al Qaeda, would instantly fill."

U.S.-backed Afghan forces overthrew the Taliban's hard-line Islamist government almost 16 years ago because it sheltered al Qaeda chief Osama bin Laden, architect of the Sept. 11, 2001, attacks on New York and Washington.

U.S. forces have been bogged down since in a war that has vexed three American presidents. About 2,400 U.S. troops have died in Afghanistan.

Trump said "our troops will fight to win", but he also stressed that ultimately Afghanistan's police and army must do most of the fighting to defeat the Taliban and allied Islamist militants.

Most of the U.S. troops in Afghanistan work with a NATO-led training and advising mission, with the rest part of a counter-terrorism force that mostly targets pockets of al Qaeda and Islamic State fighters.

NO TIMELINES

Afghan President Ashraf Ghani welcomed Trump's strategy, saying it would expand the training mission for Afghan forces, which includes building its fledgling air force and doubling the size of the Afghan special forces.

"I am grateful to President Trump and the American people for this affirmation of support ... for our joint struggle to rid the region from the threat of terrorism," he said in a statement.

The Taliban condemned Trump's decision.

"If the U.S. does not pull all its forces out of Afghanistan, we will make this country the 21st century graveyard for the American empire," Taliban spokesman Zabihullah Mujahid said in a statement.

Trump, who had criticized his predecessor, President Barack Obama, for setting deadlines for drawing down troops in Iraq and Afghanistan, declined to put a timeline on expanded U.S. operations in Afghanistan.

Obama's deadlines drastically reduced the U.S. military presence in Afghanistan from about 100,000 troops in 2011.

Mattis said lessons learned from fighting Islamic State in Iraq would be used in Afghanistan.

When asked how Trump's strategy would differ from those of previous administrations, he said the approach would be broader but provided no specifics.

In his speech, Trump said U.S. support was not a "blank check" for Afghanistan's often-divided and corruption-plagued government and insisted he would not engage in nation-building, a practice he has accused his predecessors of doing at huge cost.

Trump signaled a tough line on Pakistan, which shares a border with Afghanistan.

"We can no longer be silent about Pakistan's safe havens," he said, referring to complaints that Taliban and other militants move freely in Pakistan.

Pakistan's foreign ministry did not respond to requests for comment, but ahead of the Trump speech Pakistani army spokesman Major General Asif Ghafoor said on Monday: "There are no terrorist hideouts in Pakistan."