British Prime Minister David Cameron made separate telephone calls to US President Barack Obama, Italian Prime Minister Silvio Berlusconi and Prime Minister Hamad bin Jassim of Qatar, Cameron's Downing Street office said.
During the calls, Cameron "emphasised the urgent importance of placing continued military and diplomatic pressure on the Qadhafi regime in order to protect the many thousands of civilians who remain under attack there", a statement said.
Cameron later briefed the leaders on Britain's involvement with the Libyan Transitional National Council, the Qadhafi opposition body.
According to a statement from Obama's White House office, the pair "agreed that UN Security Council resolutions on Libya must be fully implemented" and vowed to increase economic pressure on the long-serving ruler.
The two leaders also noted the "international consensus achieved at last week's Contact Group meeting in Doha and the NATO Foreign Ministerial in Berlin, both of which emphasized the need for Qadhafi to leave power".
France and Italy joined Britain on Wednesday in sending military advisers to insurgent-held eastern Libya, as Tripoli warned that foreign boots on the ground would prolong the conflict.