Afghan Interior Ministry special forces stand guard in Kabul
Two fresh explosions and gunfire were heard from within a major foreign guesthouse complex used by international organisations in the Afghan capital Kabul Wednesday, an AFP photographer said.
The "Green Village" near the main airport was earlier rocked by a suicide car bomb attack which authorities say killed at least six people. The attack was claimed by Taliban insurgents.
Explosions rocked Kabul shortly after US President Barack Obama paid a surprise visit on the anniversary of Osama bin Laden's death.
The US embassy, which neighbours the AFP bureau in Kabul, said its embassy was "under lockdown" and warned staff to "take cover, move away from the windows".
Obama earlier dropped from night skies into Kabul on a brief visit amid secrecy and tight security and signed a deal with President Hamid Karzai, cementing 10 years of US aid for Afghanistan after NATO combat troops leave in 2014.
The explosions were a reminder of the extremist threat that stalks Afghanistan, with the Taliban resurgent a decade after they were driven from power for refusing to hand over bin Laden following the 9/11 attacks.
"Duck and cover here at the embassy. Not a drill - avoid the area," the US embassy said on Twitter.
Karzai said the US pact "is not threatening any third country, including the neighbouring countries, but we are hoping that this leads to stability, prosperity and development in the region".
"Neither Americans nor the Afghan people asked for this war, yet for a decade we've stood together," Obama said at the signing ceremony.
"We look forward to a future of peace. We're agreeing to be long-term partners," said Obama, who later headed home aboard Air Force One after just six hours on the ground.
The pact, agreed last month, sees the possibility of American forces staying behind to train Afghan forces and pursue the remnants of Al-Qaeda for 10 years after 2014.
It does not commit Washington to specific troop or funding levels for Afghanistan, though is meant to signal US foes that despite ending the longest war in US history, Washington intends to ensure Afghanistan does not revert to a haven for terror groups like Al-Qaeda.
But after a war that has cost the lives of nearly 3,000 US and allied troops, maimed tens of thousands more, saw thousands of Afghans killed and cost hundreds of billions of dollars, Afghanistan's future is deeply uncertain.