Mr Cameron's comments will carry additional diplomatic weight because they were made in Turkey, which has threatened to sever ties with Israel after its deadly assault on a flotilla carrying humanitarian aid to Gaza.
In a stopover on his way to India, Mr Cameron launched a diplomatic offensive aimed at bolstering Turkey's bid to join the European Union and enlisting its support in the efforts to stop Iran from building a nuclear bomb.
In comments that will play well in Turkey, Mr Cameron frankly addressed the situation in Gaza. Speaking to business leaders in Ankara, Mr Cameron condemned Israel's land and sea blockade of Gaza, aimed at weakening the Islamist group Hamas, which seized control of the strip in 2007.
"Let me be clear that the situation in Gaza has to change," said Mr Cameron, reiterating comments that he made earlier to the House of Commons. "Gaza cannot and must not be allowed to remain a prison camp."
Turkey's Prime Minister, Recep Tayyip Erdogan, applauded Mr Cameron's words, and repeated his condemnation of the flotilla assault in international waters, comparing it to Somali piracy.
Israel's relations with Turkey, already strained after the 2008-2009 Gaza conflict, further deteriorated when Israeli commandos boarded the lead ship of a flotilla aimed at breaching the Gaza blockade. Israeli troops killed nine activists, mostly Turks, prompting an international outcry.
Mr Cameron yesterday reiterated earlier comments that the attack was "unacceptable" and called for a "swift, transparent and rigorous" investigation of the raid.
Israel has closely linked the continuing blockade to its own security concerns and to Gilad Shalit, an Israeli soldier taken captive by Islamic militants four years ago.
"The people of Gaza are the prisoners of the terrorist organisation Hamas," said Ron Prosor, Israel's ambassador to the UK. "The situation in Gaza is the direct result of Hamas's rule and priorities."
Nevertheless, Israel conceded recently that its blockade has strengthened, not weakened, Hamas, and bowed to international pressure to allow in more goods, including some building materials.
The blockade has shattered Gaza's economy, forcing some 80 per cent of Palestinians on to international handouts. Unemployment is rife, and Israel does not allow the export of goods, forestalling any economic recovery.
Critics say that Israel's overall policy has not changed. Palestinians are still not allowed in and out, other than in exceptional circumstances, and the inflow of goods, mostly consumer, is still inadequate for Gaza's needs.
Sari Bashi, executive director of the Israeli Gisha human rights group, said Israel's policy was "collective punishment". "Innocent people are being prevented from accessing education, economic opportunities, family members and even medical care," she said.
Mr Cameron was in Turkey to woo Ankara, a strategic ally in the Middle East that has acted as an important bridge between East and West.
Throwing his support behind Turkey's stalled bid to join the European Union, he said the club would be "not stronger but weaker" for its absence. Mr Cameron added: "I'm here to make the case for Turkey's membership of the EU. And to fight for it."
Turkey's bid, however, is likely to encounter resistance from France and Germany, which have both blocked it since accession talks began in 2005. Stumbling blocks include Turkey's refusal to recognise Greek Cyprus and its treatment of the Kurdish minority.
Mr Cameron said, though, that Turkey had earned its place in the club. "When I think about what Turkey has done to defend Europe as a Nato ally, and what Turkey is doing today in Afghanistan alongside our European allies, it makes me angry that your progress towards EU membership can be frustrated in the way it has been," said Mr Cameron. "I believe it's just wrong to say Turkey can guard the camp but not be allowed to sit inside the tent."
He said that Turkey, which wants to strengthen ties with Iran, remained one of Europe's few allies who would carry influence in Tehran to prevent it from developing a nuclear weapon. "It's Turkey that can help us stop Iran from getting the bomb," he said.
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