LONDON — President Bush, ending a weeklong trip through Europe today, warmly welcomed Britain’s pledge to tighten sanctions against Iran and to send more troops to increasingly violent Afghanistan.

The president and Prime Minister Brown used a joint news conference to show solidarity on an array of vexing foreign policy matters — chiefly Iran, Iraq, and Afghanistan. Mr. Bush dismissed reports he had differences with Mr. Brown on Iraq, where Britain has cut its troops.

“I have no problem with how Gordon Brown is dealing with Iraq,” Mr. Bush said. “He’s been a good partner.”

The two leaders, both weakened by low public approval, traded compliments and emphasized common stands on such other global problems as Zimbabwe, Myanmar, and Darfur and a stalled world trade pact. They then headed to Belfast where, along with Ireland’s prime minister, Brian Cowen, they were to visit the Protestant and Catholic leaders of Northern Ireland’s power-sharing government.

At London, Mr. Brown praised Mr. Bush for his “steadfastness and resoluteness.” Said Mr. Bush of Mr. Brown, “He’s tough on terror and I appreciate it.”

The prime minister came ready with twin announcements that helped buoy Mr. Bush’s position.

Mr. Brown said Britain will freeze assets of Iran’s largest bank in a further move to discourage the country from developing nuclear weapons. And he announced that Britain was sending more troops to southern Afghanistan, upping London’s commitment to the highest level ever.

On Iran, Mr. Brown used almost the identical language that Mr. Bush has chosen in trying to build world pressure against Iran. America and other Western nations fear Iran is pursuing uranium enrichment as means to develop nuclear weaponry, a charge the Tehran government denies.

“I will repeat that we will take any necessary action so that Iran is aware of the choice it has to make — to start to play its part as a full and respected member of the international community, or face further isolation,” Mr. Brown said. He said Britain was starting a new phase of sanctions on oil and gas.

Britain’s new deployment of about 230 engineers, logistical staff, and military trainers to Afghanistan will boost the number of British forces in the country to more than 8,000, most based in Helmand province in the south.

Mr. Brown showed no distance from Mr. Bush on the strategy in Iraq. The prime minister said he would not order an arbitrary withdrawal of the 4,000 remaining British troops until the task is done, and there would be no trade-off by moving troops out of Afghanistan.

“In Iraq there is a job to be done and we will continue to do the job and there will be no artificial timetable,” Mr. Brown said.

Britain has 4,000 troops remaining in Iraq on the outskirts of Basra. British forces withdrew from their base in Basra’s city center last year and began to focus only on training Iraqi security forces. Britain suspended plans to remove another 1,500 troops after fighting broke out in Basra in March — a development Mr. Bush highlighted today as a positive sign that Mr. Brown would only yank out troops as conditions merited.

Questioned about his own reflections on Iraq, Mr. Bush offered no apologies.

He said that history will judge how America waged the war — whether more troops should have been deployed and whether they should have been positioned differently. But he said he had no doubts about deposing Iraqi leader Saddam Hussein. “Absolutely it’s necessary,” the president said.

Mr. Bush also chided leaders of other major industrialized nations for not fully keeping their promises to funnel aid into Africa. He said his message at next month’s summit of the Group of Eight industrialized nations in Japan will be: “Just remember, there are people needlessly dying on the continent of Africa today, and we expect you to be more than pledge-makers. We expect you to be check-writers for humanitarian reasons.”

The president, without getting specific, said America can help calm mounting tensions between Afghanistan and Pakistan.

He spoke sympathetically of the conditions that led Afghanistan’s president, Hamid Karzai, to threaten to send troops into Pakistan as a means to target terrorists. But he stopped short of endorsing any such cross-border incursion.

“Obviously, it’s a testy situation there,” Mr. Bush said. “And if I’m the president of a country and people are coming from one country to another — allegedly coming from one country to another — to kill innocent civilians on my side, I’d be concerned about it.”

Mr. Karzai said yesterday that Afghanistan has a right to send troops into Pakistan because Taliban militants cross over from Pakistan to attack Afghan and foreign forces. Mr. Bush called for leaders of Afghanistan and Pakistan to hold talks and share intelligence as both confront notorious Taliban leaders.

In the brutal standoff in the African nation of Zimbabwe, Mr. Brown called on President Mugabe to allow a United Nations human rights envoy as well as election monitors to enter the country. “Mugabe must not be allowed to steal the election,” he asserted.

Mr. Mugabe faces opposition leader Morgan Tsvangirai in a June 27 presidential runoff. Opposition supporters say they have been arrested, burned out of their homes, beaten, and killed. Diplomats trying to investigate the violence have been harassed by police.

Mr. Bush praised the prime minister’s strong words and said America would work with Britain to try to achieve fair elections.