Afghanistan's upper house of parliament on Thursday approved two agreements with the US and NATO allowing about 12,500 troops to remain in the country next year as concerns grow over the worsening insurgency.

The Bilateral Security Agreement (BSA) with the United States, and a similar pact with NATO, were approved by the lower house of parliament on Sunday before being sent to the senate.

Both documents were the source of huge friction between the Afghan government and its allies under previous president Hamid Karzai.

But President Ashraf Ghani, who came to power in September, reset ties by signing the long-awaited deals on his first day in power.

"We approved both documents today," Belgis Roshan, a senator, told AFP.

Qadamuddin Nekpa, a parliamentary media officer, said only seven MPs voted against the deals.

NATO Secretary General Jens Stoltenberg welcomed the ratification, saying it meant the alliance "now has the legal basis needed to move forward with our non-combat mission to train, advise and assist the Afghan National Security Forces from 1 January".

US-led NATO combat operations will finish at the end of this year, but the Taliban have launched a series of recent offensives and suicide attacks that have severely tested Afghan soldiers and police.

On Thursday, a suicide bomber rammed his explosives-packed car into a British embassy vehicle in Kabul, killing one British citizen and at least five Afghans.

Five children were among more than 30 bystanders injured in the blast, officials said.