Gambia - which is a long thin sliver of land surrounded by Senegal - has a stranglehold on the best routes between one part of Senegal and the other.

Relations between the two countries have become increasingly frayed since a row over increased ferry charges erupted in August.

On Tuesday, some Senegalese soldiers were briefly held in Gambia's capital.

The group of soldiers were taking the shortest route between northern Senegal and its southern region, Casamance, which cuts across The Gambia - and doing a little shopping on the way.

They were detained in Banjul market, and taken off to answer questions about what Senegalese soldiers were doing in The Gambia, armed and in uniform, without permission.

They had crossed by the Banjul ferry, at the mouth of the Gambia River.

The Trans-Gambia Highway, which runs further inland, has effectively been closed to cross-border traffic for over a month by Senegalese transporters protesting against the sudden doubling of charges to cross the river on the small and unreliable ferry.

The BBC's Elizabeth Blunt says that Senegalese hate the power The Gambia has over them, and a clearly exasperated President Abdoulaye Wade this week suggested three ways to break the deadlock.

• Gambia should build a bridge over the river

• Senegal could operate its own ferry

• Senegal could even, he suggested, tunnel right under The Gambia - which is only about 35km wide.

He pointed out that there are plenty of much longer tunnels in the world, and claimed that China had offered to help build it.