US President Donald Trump unveiled late on Monday his administration’s long-awaited new strategy on Afghanistan, committing to an open-ended conflict in the country. He signaled that he would send more troops to Afghanistan, vowing a “fight to win” against Taliban insurgents, who have gained ground against the US-backed Afghan government. Trump also singled out Pakistan for harboring militants. "We are not nation-building again. We are killing terrorists," he said in a prime-time televised address at a military base outside Washington. Trump ran for the US presidency calling for a swift US withdrawal from Afghanistan, and he acknowledged on Monday that he was going against his instincts in approving the new campaign plan sought by his military advisers. "The consequences of a rapid exit are both predictable and unacceptable," he said. "A hasty withdrawal would create a vacuum that terrorists, including ISIS and al-Qaeda, would instantly fill." The Republican president, who has criticized his predecessors for setting deadlines for drawing down troops in Iraq and Afghanistan, declined to put a time line on expanded US military operations in Afghanistan. Afghanistans government applauded Trumps speech for focusing on needs and conditions instead of timelines. Afghan Ambassador to the US Hamdullah Mohib calls it a "10 out of 10." He told The Associated Press by telephone from Kabul that Afghans heard "exactly what we needed to." Mohib said critiques of the speech for failing to disclose troop numbers are misguided. He added that the focus on numbers detracts from the "real focus" on conditions and support needed for Afghanistan to succeed and achieve peace. The ambassador stated that Afghanistan has made progress and is committed to pursuing reforms to show it merits continuing help from the US. Trump now inherits the same challenges as predecessors George W. Bush and Barack Obama, including a stubborn Taliban insurgency and a weak, divided government in Kabul. He is laying the groundwork for greater US involvement without a clear end in sight or providing specific benchmarks for success. Trump warned that US support "is not a blank check," and insisted he would not engage in "nation-building," a practice he has accused his predecessors of doing at huge cost. US officials said he had signed off on Defense Secretary James Mattis plans to send about 4,000 more troops to add to the roughly 8,400 now deployed in Afghanistan. Mattis said he had directed the chairman of the Joint Chiefs of Staff to carry out the strategy and that he would be consulting with NATO and US allies, several of which had also committed to increasing troops. Trump saved his sharpest words for Pakistan. "We can no longer be silent about Pakistan’s safe havens," Trump said. "Pakistan has much to gain from partnering with our effort in Afghanistan. It has much to lose by continuing to harbor terrorists." A Pakistani army spokesman said on Monday that Pakistan had taken action against all extremist militants including the Haqqani network, which is allied to Afghan Taliban insurgents. "There are no terrorist hideouts in Pakistan. We have operated against all terrorists, including (the) Haqqani network," spokesman Major General Asif Ghafoor told a media briefing in Islamabad. A US-led coalition invaded Afghanistan and overthrew the Taliban government for harboring al-Qaeda militants who plotted the September 11 attacks. But US forces have remained bogged down there through the presidencies of Bush, Obama and now Trump. About 2,400 US forces have died in Afghanistan since the invasion. US military and intelligence officials are concerned that a Taliban victory over Afghan President Ashraf Ghanis government would allow al-Qaeda and ISIS’ regional affiliate to establish bases in Afghanistan from which to plot attacks against the United States and its allies. In Kabul, Taliban spokesman Zabiullah Mujahid dismissed Trumps speech as "old" and his policy as "unclear." Last week the Taliban issued a 1,600-word open letter to Trump warning against a troop surge, saying it would prolong what is already the United States longest war. Trump steered clear of discussing troop numbers, but said US forces are in Afghanistan to win. The Taliban have also said they arent ready for any peace talks, at least not until the US and NATO give a time frame for withdrawal — something Trump says isnt going to happen. Britain on Tuesday welcomed Trump’s speech. "The US commitment is very welcome," British Defense Secretary Michael Fallon said in a statement. "Its in all our interests that Afghanistan becomes more prosperous and safer: thats why we ‎announced our own troop increase back in June."