A political crisis in The Gambia appears to be coming to a head, with Senegalese troops massed on the border after a deadline for President Yahya Jammeh to step down passed with no apparent change of heart from him. Mr Jammeh has refused to hand over power after losing elections last month, while his victorious challenger, Adama Barrow, is preparing to be sworn in.
What happens next?
Mr Barrow, who is in neighbouring Senegal, had hoped to be inaugurated as president at the national stadium in The Gambia, but that plan has had to be abandoned because of Mr Jammeh's intransigence. He will now be sworn in at the Gambian embassy in Senegal and is expected to be recognised internationally as his country's head of state.
How soon he is able to take power in his country remains unclear. West African regional grouping Ecowas has mandated Senegal, which almost surrounds The Gambia, to lead a military intervention to install Mr Barrow. Nigeria has sent aircraft and troops to Senegal, and deployed a warship.
However, West African military sources say intervention is intended only as a last resort if Mr Jammeh cannot be persuaded by the threat of force to stand aside. "If no political solution is found, we will step in," Col Abdou Ndiaye, a spokesman for the Senegalese military, was quoted by Reuters news agency as saying.
Gambia is a popular tourist destination and after the British Foreign Office updated its travel advice, holiday companies have started evacuating tourists.
Would military intervention be legal?
Senegal has circulated a draft resolution at the UN Security Council, seeking authorisation for an intervention but no vote has been scheduled. Some diplomats have suggested that such authorisation may not be necessary if Mr Barrow is sworn in, recognised internationally as head of state and requests help.
What is Mr Jammeh's position?
Having refused to give up power, Mr Jammeh tried to bolster his position earlier this week by declaring a state of emergency and engineering a parliamentary vote to extend his presidency by three months. He said these moves would prevent a power vacuum while the Supreme Court considered a legal challenge he has submitted over the election result.
Apparently disregarding the possibility that the court could eventually rule against him, he has also promised to stay in power until new elections can be held.
Although the parliamentary vote took place while Mr Jammeh was still officially president, regional powers are not regarding the decision as valid and are continuing with their plans to install Mr Barrow. Without this extension, Mr Jammeh's term ended at midnight on Thursday.
Would military intervention succeed?
A Senegalese-led intervention force would be expected to have more firepower than the Gambian army but it is not clear how much resistance it would face.
The army chief is a close Jammeh loyalist but has been quoted as saying he would not risk his men's lives in a political dispute.
The elite regiment of the army, drawn mainly from the same ethnic group as Mr Jammeh, is well-armed and is regarded as being fiercely loyal. However, it would be at a considerable numerical disadvantage to an intervening force.
The loyalty of other regiments is much less certain. Correspondents say there has been talk that some are unhappy with recent events and want a peaceful resolution.
How are the Gambian people reacting?
Tension is high in the Gambian capital, Banjul, over concerns that the political conflict will escalate into violence. Thousands of people have fled to neighbouring countries and rural areas.
Earlier this week, Mr Barrow's coalition urged Gambians to "exercise restraint, observe the rule of law and not to respond to provocation".
The BBC's Umaru Fofana, who is in Banjul, says people there are petrified. They are stocking up on food and water. Everyone is praying for a peaceful resolution, he says.
What is the dispute over the election?
Mr Jammeh, who seized power in a 1994 coup, initially accepted that Mr Barrow had won the election but later reversed his position and said he would not step down.
He filed a petition to the Supreme Court, challenging the election results, and says the existence of this legal process means it would be unconstitutional for Mr Barrow to assume office.
He also asked the Supreme Court for an injunction to stop the inauguration but the chief justice declined to rule on it, saying he must recuse himself from any case that could affect his own position - he would normally conduct the swearing-in ceremony.
Mr Jammeh has said there were irregularities in the election process, including the turning away of some of his supporters from polling stations, and errors made by the electoral commission.
The commission accepted that some of the results it initially published contained errors, but said Mr Barrow still won.
Retaining power would ensure he was not prosecuted in The Gambia for alleged abuses committed during his rule.
How have his allies reacted to the crisis?
Ministers are continuing to desert Mr Jammeh's government. Several ministers, and even the long-serving vice-president, have resigned in recent days.
One of the ministers who resigned, former information chief Sheriff Bojang, said Mr Jammeh's arguments had a "veneer of constitutionalism" but were an attempt to subvert the will of the Gambian people. The international community says Mr Barrow won fairly.
The lawyer representing Mr Jammeh and his APRC party in the election challenge has also fled to Senegal and urged the long-time leader to step aside.
What is happening at the Supreme Court?
Judges from Nigeria and Sierra Leone have been hired to hear the petition to overturn the election result, but they have yet to arrive in Banjul.
Gambian chief justice Emmanuel Fagbenle has said the court will be able to convene no earlier than May, and possibly not until November, because the Nigerian who is to act as court president, Onogeme Uduma, is fully booked for the coming months.
How might this be resolved?
Mr Barrow has distanced himself from comments, made by other opposition figures, suggesting Mr Jammeh may be prosecuted over alleged abuses in power.
He said Mr Jammeh should be able to stay in The Gambia and would be honoured as, and receive the privileges of, a former head of state if he stepped down.
However, analysts say Mr Jammeh is unlikely to be persuaded by his opponent's apparently conciliatory language.
Another option, raised by Nigerian MPs, is that Mr Jammeh could be offered asylum and a comfortable retirement in another African country.
Besides Nigeria, Morocco has been mooted as a possible destination (Mr Jammeh's wife is Moroccan).
A third possibility has been made more likely by Mr Jammeh's recent moves - that, in the absence of a clear court ruling, Mr Jammeh continues to cling to power with army backing, pending military intervention by regional powers.