The commander of US and Nato forces in Afghanistan has said he needs a "few thousand" more troops to break a stalemate in the war with the Taliban.
Gen John Nicholson told the US Senate Armed Services Committee he had enough forces for counter-terror operations.
But he stressed extra troops were needed to help train the Afghan military. The soldiers, he said, could be American or from other Nato nations.
He accused Russia and Iran of trying to undermine Nato in Afghanistan.
Testifying before the Senate committee on Thursday, Gen Nicholson said: "We have a shortfall of a few thousand."
He said he had already discussed the issue with President Donald Trump's new Defence Secretary, James Mattis.
There are currently about 8,400 US troops in Afghanistan in the 13,300-strong Nato contingent.
US combat operations against the Taliban officially ended in 2014 - but special forces have continued to provide support to Afghan troops.
Afghan forces have suffered thousands of casualties in the past two years.
Gen Nicholson described the current security situation in the country as a "stalemate", but added that the "equilibrium favours the government".
And he also expressed concerns about "the influence of external actors - particularly Russia, Pakistan and Iran".
He said this influence continued to "legitimise and support the Taliban and undermine the Afghan effort to create a stable Afghanistan".
Russia - which has recently invited a Taliban delegation for talks in Moscow - argues that its support for the Taliban helps to combat so-called Islamic State.
But Gen Nicholson said it was a "false narrative".