Demonstrators were to rally in London on Friday to protest against Britain's failure to bring about a ceasefire in the Middle East conflict.
The Friends of Lebanon group were to demonstrate outside the heavily-guarded US embassy at midday (1100 GMT).
And at 5:00 pm (1600 GMT), the Palestine Solidarity Campaign (PSC), Stop the War Coalition, Campaign for Nuclear Disarnament and the British Muslim Initiative were to protest outside the Downing Street offices of Prime Minister Tony Blair, despite his absence.
The British premier is on holiday in Barbados, having delayed his departure to stay in touch with other world leaders about the war between Israel and the Hezbollah militia in Lebanon.
"The killing cannot be allowed to continue, PSC campaigns officer Sarah Colborne told AFP.
"It's part of putting pressure on the British government to end its silence."
Protesters were to call for an immediate and unconditional ceasefire in the deadly conflict which will be one month old on Saturday.
They were to lay wreaths of flowers outside Downing Street to commemorate the lives lost -- more than 1,000 in Lebanon and more than 100 Israelis so far.
Foreign Secretary Margaret Beckett abandoned her European camping trip to fly to New York on Thursday in an attempt to push for a United Nations resolution aimed at bringing about a lasting ceasefire.
On Sunday, a crowd of 20,000 organised by the Stop the War Coalition marched through London to demand an end to the Israeli offensive.
In the Middle East, Israeli planes blasted targets far into the north of Lebanon on Friday as their ground troops held off on a threatened major offensive in the south and Russia threw a wild card into the protracted haggling over a truce call at the United Nations.