UK Foreign Secretary William Hague has condemned the killing of a Briton by Islamist militants in Algeria as "cold-blooded murder".
Algeria says one of its citizens also died at a gas facility on Wednesday and about 20 foreign workers, including Britons, are now being held hostage.
Mr Hague said the UK and Algeria were working "round the clock" to resolve the crisis.
Ghana News Headlines
For latest news in Ghana, visit Graphic Online news headlines page Ghana news page
The government's emergency committee Cobra has discussed the situation.
The Foreign Office said a "rapid deployment team" had been sent "to reinforce British embassy and consular staff in Algeria" and it was "liaising very closely with all levels of the Algerian government".
Algerian troops have surrounded the complex at In Amenas, in the east of the country, operated by state oil company, Sonatrach, along with Britain's BP and Norway's Statoil.
The other captives are said to include Japanese, US, French and Norwegian nationals.
In a statement, BP said: "The situation on site remains unresolved and fragile. Armed groups still occupy the site and hold a number of site personnel."
Militant groups have vowed to avenge France's military intervention in Mali, where its forces have been battling Islamists linked to al-Qaeda in the Islamic Maghreb (AQIM) for the past week. Algeria has been allowing French aircraft to use its air space.
But speaking during a visit to Australia, Mr Hague cast doubt on claims the incident was linked to Mali, saying: "That is a convenient excuse, but usually operations like this take longer to plan."
He added: "Whatever excuse is being used by terrorists and murderers who are involved, there is no excuse for such behaviour...
"This is the cold-blooded murder of people going about their business."
Mr Hague said: "The safety of those involved and their co-workers is our absolute priority and we will work around the clock to resolve this crisis."
Algerian Interior Minister Daho Ould Kabila said the militants, who claim they are holding 41 people, wanted to leave the country with the hostages, but he had refused to let them go.
He said the kidnappers were Algerian and operating under orders from Mokhtar Belmokhtar, a senior commander in AQIM until late last year, when he set up his own armed group after apparently falling out with other leaders.
The Algeria Press Service has reported that 30 Algerian workers, who were also being held hostage, escaped from the facility. And Ennahar television said that 15 foreign hostages were now also safely out of the area. The reports have not been independently confirmed.
Prime Minister David Cameron chaired three Cobra meetings on Wednesday to discuss the incident and Downing Street said he later "expressed his sympathy and support" when he spoke to his Algerian counterpart Abdelmalek Sellal.
BP chief executive Bob Dudley said: "BP's overriding priority is to do all we can to ensure the safety of our staff and to support their families during this anguishing time.
"We will remain in frequent contact with the families to provide support and update them on developments."