At least 100 deaths have been reported in an Ebola outbreak in the Democratic Republic of Congo, with more than 390 cases suspected, the head of the Africa Centres for Disease Control and Prevention has told the BBC.

The World Health Organization (WHO) has declared the outbreak an international emergency.

The current strain of Ebola is caused by the Bundibugyo virus, for which there are no approved drugs or vaccines.

There are also two confirmed cases and one death in Uganda, according to the US Centers for Disease Control and Prevention (CDC).

At least six Americans have been exposed to the Ebola virus during the outbreak in the DR Congo, sources have told CBS News, the BBC's US partner.

One American is believed to have symptoms, with three others said to have faced a high-risk contact or exposure. It is unclear whether any have been infected.

The CDC said it was supporting the "safe withdrawal of a small number of Americans who are directly affected", but did not confirm how many.

The US government is reportedly looking to arrange transport for the small group of Americans in DR Congo to a safe quarantine location, a source told health news site STAT.

Quoting a source, the site adds that the group could be taken to a US military base in Germany, though this has not been confirmed.

The CDC declined to answer direct questions about the US citizens reportedly affected during a press conference on Sunday.

In an update on Monday, the public health agency said the risk to the US was relatively low, but said it would introduce a range of measures to prevent the disease from entering the country.

This includes monitoring travellers arriving from affected areas and placing entry restrictions on non-US passport holders if they have been in Uganda, DR Congo or South Sudan in the last 21 days.

The CDC said it would work with airlines and other partners to carry out contact tracing of passengers, increase testing capacity and hospital readiness to respond to the outbreak.

The US has also issued a Level Four travel advisory - its most severe level - warning against travel to the DR Congo.