Britain's international development minister Mike Foster is set to visit Sri Lanka.
It comes after Gordon Brown pledged an extra £2.5 million for humanitarian aid to help people displaced by the fighting in the country's northern war zone.
Downing Street said the PM had spoken to Sri Lankan president Mahinda Rajapaska to raise his concerns about the plight of civilians in the conflict area, while reiterating calls for a ceasefire.
Since last Monday more than 100,000 people have fled the northern coastal strip still held by the Tamil Tiger rebels as the Sri Lankan military continues its offensive to destroy the group and end the island's long-running civil war.
Sir John Holmes, United Nations Commissioner for humanitarian affairs, is currently visiting the island in an attempt to persuade the government to allow aid into the conflict zone where an estimated 50,000 people remain trapped.
The Tamil Tiger rebels announced on Sunday a unilateral ceasefire but it was rejected by the government.
A Downing Street spokesman said: "The Prime Minister has spoken to Sri Lanka's President Rajapaksa. The Prime Minister said he remained concerned about the plight of civilians in the conflict zone.
"He repeated his call for a ceasefire, and pledged a further £2.5 million for humanitarian aid for displaced persons."
Mr Foster will conduct a humanitarian assessment before Foreign Secretary David Miliband joins his French and Swedish counterparts on a trip to the island on Wednesday, the spokesman said.
President Rajapaska has also invited Sri Lanka envoy Des Browne and a cross-party group of MPs to visit soon, he added.
