The United States won't attend a multinational peace conference on Afghanistan next month in Russia, a State Department official said Thursday.

The reasons: The US wasn't consulted before receiving the invitation and doesn't know Russia's objectives for the gathering.

The official said that Washington wants to work with Moscow on regional efforts to end the 16-year war, and that Secretary of State Rex Tillerson would bring up the matter when he visits Russia in April. The official wasn't authorised to speak publicly on the matter and demanded anonymity.

Afghanistan, Pakistan, Iran, India and several Central Asian nations are among the invitees to the Moscow conference. Afghan and US officials say the Taliban aren't invited. The State Department hasn't publicly announced its position on the planned conference.

Last year, Pakistan, Afghanistan, China and the United States met to jump-start the peace process but that effort faltered.

The official said the US wants nations in the region, which have a shared interest in peace in Afghanistan, to increase pressure on the Taliban to negotiate with the Afghan government.

Last week, Pakistani officials hosted seven Taliban leaders in Islamabad to try to press the insurgents into peace talks ahead of the Moscow meeting, two Taliban officials told the AP.

Islamabad has been under international pressure to try to bring Taliban leaders, who have lived in Pakistan since their rule in Afghanistan was overthrown in the 2001 US invasion, into some form of negotiations with Kabul.

In Washington on Tuesday, Afghan Foreign Minister Salahuddin Rabbani called for the US to add to the 8,400 troops currently in Afghanistan where the Taliban have stepped up attacks and the Islamic State group also poses a threat.

He said the Afghan government remains open to peace talks but doubted the Taliban would participate unless Pakistan cracked down on “terrorist safe havens” on its soil a long-running source of bitterness between the neighbouring countries.